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Phantom smells may be a sign of trouble
Problems with our sense of smell, including phantom odors or a loss of smell, can be a warning sign of serious illness.
Since the beginning of the pandemic, Covid infection has been the main culprit for causing a loss of smell or taste. Although most recover within a month or so, about 5% of people with a confirmed case of Covid report smell and taste dysfunction six months later, according to a study published in July.
Before a full recovery, many patients who have Covid-related loss of smell describe a period when they experience phantom smells like burning rubber or smoke or other foul odors that aren't really there, the researchers report. Covid is also linked to a condition known as parosmia, which turns a pleasant odor such as coffee into an unpleasant one.
For people who have mostly recovered from Covid but are still coping with a loss of smell, scientists from Duke Health found some new clues from biopsies taken deep inside nasal cavities. There's evidence of continued inflammation and an immune response persisting months after an infection.
Normally, we experience smell when the olfactory sensory neurons in the nose pick up an odor and then transmit a message to the brain, which identifies the odor. Another way for the brain to receive information about an odor is through a channel that connects the top of the throat to the nose. When we chew food, aromas are released that pass through the channel to the olfactory sensory neurons, then to the brain.
Viruses including flu, parainfluenza and other coronaviruses, along with other health issues, can lead to smell dysfunction, said rhinology expert Dr. Jonathan Overdevest, an assistant professor of otolaryngology and head and neck surgery at Columbia University Irving Medical Center in New York.
“Alterations in one’s sense of smell can be the result of chronic sinusitis,” said Overdevest. "The ongoing inflammation can in time impair the sense of smell or cause smell loss. If a dental infection is causing the sinusitis, people may sense a foul smell.”
Beyond Covid, smelling something that isn't there can indicate a serious condition.
A 2018 study found that millions of Americans may have some kind of olfactory disorder, reporting unpleasant, bad or burning odor when no actual odor is there. The researchers from the National Institute on Deafness and Communication Disorders, part of the National Institutes of Health, found a link to depression, migraine auras and head trauma.
“A head trauma that shears the connection between the brain and the peripheral nerves in the nose can lead to a loss of smell," Overdevest said.
Neurodegenerative diseases, such as Alzheimer’s and Parkinson’s, can also lead to problems with smell, including phantosmia, according to the National Institute on Deafness and Communication Disorders (NIDCD).
“When someone is smelling something and there is no source of that smell, similar to when people have phantom limb pain, it’s called phantosmia,” said Stephanie Hunter, a postdoctoral fellow at the Monell Chemical Senses Center in Philadelphia. “It’s thought that this might be caused by overactive neurons."
People who suffer with a smell disorder may lose weight, since smell and taste are so closely linked, although others may eat too much and gain weight or use too much salt.
Commonly reported phantom smells are bad, such as rotten eggs or burning hair.
Types and causes of smell disorders
The causes of smell disorders are not well understood, but women seem to be affected twice as often as men, according to the NIDCD study. Normal aging is also associated with some loss of smell or taste.
About 2% of Americans have some type of olfactory problem, including:
- Anosmia, the inability to smell.
- Hyposmia, a decreased ability to smell.
- Parosmia, a distorted perception. Coffee may smell like sewage, for example.
- Phantosmia , sensing an odor that isn't there.
Loss of taste comes when a person loses the sense of smell and then is left only with the basics that come through the tongue: sweet, sour, salty, bitter and umami. Some of the taste disorders, include:
- Ageusia, the inability to taste.
- Hypogeusia, a decreased ability to taste.
- Dysgeusia, a distorted ability to taste.
Sometimes, people with a smell disorder can interpret something like urine or feces as a pleasant odor.
"We don’t hear about this as much as unpleasant smells," said Hunter. "Maybe people smelling pleasant smells are less likely to look for help.”
Smell disorders can be diagnosed and treated by an otolaryngologist, or ENT, who specializes in ear, nose, throat, head and neck diseases.
Smell training can help someone with a disorder get back to normal, Hunter said. During the training, which should last at least three months, the patient is introduced to four strong odors — rose, eucalyptus, lemon and cloves.
"You smell the odor and then try to remember what it smelled like before you lost your sense of smell," Hunter said. "It can be really frustrating and a lot of people give up. But it’s important to stick with it.”
Linda Carroll is a regular health contributor to NBC News. She is coauthor of "The Concussion Crisis: Anatomy of a Silent Epidemic" and "Out of the Clouds: The Unlikely Horseman and the Unwanted Colt Who Conquered the Sport of Kings."
Jane Weaver is managing editor of the health and medical unit at NBC News.
Why Covid-19 Patients Are Suffering From Distorted and Phantom Smells
An increasing number of patients are reporting awful scents that aren’t present
On a perfect August night, Carol Pitz, a career consultant from Chanhassen, Minnesota, was looking forward to her 25th wedding anniversary dinner, especially because she and her family had spent much of the spring isolating after exhibiting symptoms of Covid-19. She woke up one morning in March, and couldn't smell or taste anything, then developed a mild cough and fatigue. Not sick enough to be tested at the time, she and her family later tested positive for antibodies to SARS-CoV-2.
Months later, Pitz and her husband were seated at a table overlooking the lake at her favorite restaurant. She ordered the special sea bass and Brussel sprouts, and the dish looked lovely when it arrived. But after a few bites, Pitz had to stop eating. Instead of smelling her food, she was overcome by a foul, and hard-to-describe scent. “It's a unique smell,” she says. “I don't even know what it is. It's like a combination of burnt toast, and something just icky enough to make me sick to my stomach.”
What happened to Pitz is not unique. Of more than 4,000 respondents to a multilingual, international study of people with recent smell loss published in Chemical Senses in June, 7 percent reported parosmia, or odor distortion. Facebook support groups dedicated to parosmia and phantosmia, the clinical names for specific smell disorders, have grown drastically in the past few months. Instead of a scentless world, an increasing number of people who lost their sense of smell because of Covid-19 are complaining that things just don’t smell right.
They no longer wake up and can’t smell the coffee; because of parosmia, their coffee smells like burning rubber or sewage. Parosmia is most often an unpleasant smell, a distortion of an actual odor, making many foods smell and taste revolting. Phantosmia is more random, occurring without a scent trigger, uninvited and unwanted. Phantosmias, which can be fleeting or linger, are also usually foul smells, often cigarette smoke or burning wood—or for one poster on Reddit , “everything smells like a more disgusting version of Spaghetti O’s.”
Zara M. Patel, the director of endoscopic skull base surgery at the Stanford School of Medicine, has been studying olfactory dysfunction for more than a decade. It’s not unusual, she says, for smell distortions to accompany or follow smell loss. “There are so many viruses that can cause smell loss, not only other coronaviruses, but also influenza viruses and rhinoviruses,” she says. “Many of these viruses also will lead to a parosmia and phantosmia, either as part of the initial deficit, or as the nerves try and recover, but make aberrant connections.”
Smell loss, or anosmia, is such a prevalent symptom of Covid-19 it can be used for diagnosis. A May study in the Annals of Internal Medicine found 86 percent of the Covid-positive patients experienced smell loss. Most people who suffer from sudden onset anosmia from the SARS-CoV-2 infection recover their smell quickly, within four weeks for 89 percent of those in a recent study in JAMA Otolaryngology . But the remaining 10 percent continued to experience smell loss or distortions.
Researchers worldwide have been working at warp speed to unravel the mysteries of the SARS-CoV-2 virus in a flurry of preprints and shared data, with a spotlight on the chemical senses, a niche and often overlooked area of study. Early in the pandemic, researchers found that the virus needs to latch on to two proteins, ACE2 and TMPRSS2, found in many parts of the body, including the nose. This suggested that the virus could damage the olfactory neurons which relay aroma information from nose to brain. This July in Science Advances , researchers from Harvard Medical School reported that through bulk sequencing of mouse, non-human primate and human olfactory cells, they located a source of these proteins on the sustentacular cells, which support the olfactory receptor neurons and help transport odor information through the nasal mucus.
“SARS-CoV-2 binds to ACE receptors, which are present in the basal cells, supporting cells and perivascular cells around the neurons in the olfactory epithelium,” says Patel. “So although the neuron itself is not damaged, all the support structure around it is.”
“Those cells that support the regenerative capacity are the ones that suffer,” she says. “We also know that nerves do not function very well within an inflammatory environment. So because of all those reasons, it is not surprising this virus causes smell dysfunction.”
The good news, says Nancy Rawson, vice president and associate director at Monell Chemical Senses Center, a non-profit interdisciplinary research institute in Philadelphia, is that cells in the olfactory epithelium can regenerate after they have been damaged. But that regeneration can take time—up to two years, or more. “If it's affecting mature neurons, then the immature neurons need to mature fully and connect to the olfactory bulb,” she says. “Then the next wave of neurons needs to be generated to continue that process.”
Rawson says that because the brain is receiving incomplete smell information, “when the recovery process is happening in patches, or recovery is partial in different regions, you may go through that stage of parosmia on the way to a fuller recovery.”
The foul smells that characterize parosmia and phantosmia are often triggered by certain foods or smells. According to the first large study of patients with parosmia , published in 2005, the main culprits are gasoline, tobacco, coffee, perfumes and chocolate. For Pitz, coffee, chocolate and red wine smell and taste awful.
Cincinnati resident Nick Roosa shares the same triggers. He started a Facebook Covid-19 smell loss support group after he lost his sense of smell in March. He began suffering from parosmia about two months ago and says, “any food cooked with vegetable oil such as tortilla chips, French fries, chicken wings, tater tots—basically a typical American restaurant's appetizer menu—has a good chance of triggering these smell distortions.”
As of now, doctors have little relief to offer. In the past, clinicians have deployed antipsychotic, antimigraine, and antiseizure medications, corticosteroids, transcranial stimulation and even topical cocaine for relief from phantosmia and parosmia. An international group of olfactory experts writing in Rhinology advised that no definitive evidence can be found for the efficacy of any specific medical treatment for smell disorders.
But breakthroughs may be forthcoming. Because of the prevalence of smell disorders with Covid-19, more groups are showing interest in the chemosensory sciences. A global coalition of 500-plus scientists have formed the Global Consortium of Chemosensory Researchers , dedicated to open science, data sharing and interdisciplinary research to investigate the connection between the chemical senses and Covid-19. A team at Georgia State University compiled datasets of more than 602 million individual tweets about Covid-19 symptoms since March 10 that are openly available. The Mount Sinai Center for Post-COVID Care in New York is addressing “long-hauler” smell disorders in a clinical trial of fish oil. In the United Kingdom, Jane Parker, an associate professor of flavor chemistry at the University of Reading , is studying the chemistry of parosmia triggers in a research project with AbScent, a smell loss charity.
It’s been six months since Pitz lost her sense of smell, and three months since she developed parosmia. She has started to accept the changes, but laments, “People don’t understand,” she says. “The emotional parts of it are really hard to explain … when some of your favorite parts of life, like chocolate and coffee, are now all so distorted.”
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- Published: 29 September 2022
Phantom smells: a prevalent COVID-19 symptom that progressively sets in
- Christophe Bousquet ORCID: orcid.org/0000-0003-1650-8004 1 na1 ,
- Kamar Bouchoucha 1 na1 ,
- Moustafa Bensafi ORCID: orcid.org/0000-0002-2991-3036 1 na2 &
- Camille Ferdenzi ORCID: orcid.org/0000-0001-5572-0361 1 na2
European Archives of Oto-Rhino-Laryngology volume 280 , pages 1219–1229 ( 2023 ) Cite this article
One of the long-term symptoms of COVID-19 is phantosmia, a type of Olfactory Disorder (OD) that has deleterious impacts on patients’ quality of life. The aim of this article was to study how this poorly understood qualitative OD manifests itself in the COVID-19.
4691 patients with COVID-19 responded to our online questionnaire focusing on COVID-19-related OD. We first analyzed the prevalence of phantosmia in this population. Then, with the help of Natural Language Processing techniques, we investigated the qualitative descriptions of phantom smells by the 1723 respondents who reported phantosmia.
The prevalence of phantosmia was of 37%. Women were more likely to report phantosmia than men, as well as respondents for whom OD was described as fluctuating rather than permanent, lasted longer, was partial rather than total and appeared progressively rather than suddenly. The relationship between OD duration and phantosmia followed a logarithmic function, with a prevalence of phantosmia increasing strongly during the first 2 months of the disease before reaching a plateau and no decrease over the 15 months considered in this study. Qualitative analyses of phantosmia descriptions with a sentiment analysis revealed that the descriptions were negatively valenced for 78% of the respondents. Reference to “tobacco” was more frequent in non-smokers. Source names and odor characteristics were used differently according to age and OD duration.
The results of this descriptive study of phantosmia contribute to the current efforts of the medical community to better understand and treat this rapidly increasing COVID-19-related OD.
Working on a manuscript?
Quantitative Olfactory Disorders (ODs) are some of the earliest symptoms of COVID-19 [ 1 , 2 ], as well as one of the longest lasting once acute symptoms of the disease have been cured [ 3 , 4 ], inducing a reduction in the quality of life of patients [ 5 ]. Besides quantitative ODs, qualitative ones are also reported. These are parosmia (when olfactory sources smell differently than usual) and phantosmia: phantom smells are strange subjective experiences—olfactory hallucinations—occurring when no odor source is present in the environment [ 6 ]. These qualitative disorders often have an even more deleterious impact on daily life than the quantitative partial (i.e., hyposmia) or total (i.e., anosmia) loss of smell [ 6 , 7 ], even though patients rarely seek medical support [ 8 ]. Research on COVID-19-induced OD reports that both parosmia and phantosmia become more prevalent as OD duration increases [ 9 , 10 , 11 ]. It has even been found that they can appear after a period of apparent recovery from COVID-19-induced OD [ 12 ].
Before the wake of the COVID-19 pandemic, research on phantosmia was not very advanced, potentially due to the subjective nature of this sensory phenomenon. However, coupled with research on other forms of sensory hallucinations, a few findings have emerged. First, the prevalence of phantosmia varies depending on the studies and the populations investigated (from 6.5% of the general population in , to 10% of Parkinson’s patients in , and 25.6% of patients with chemosensory and nasal/sinus complaints in ). This figure rises to 50% for patients suffering from head trauma or post-viral upper respiratory infections [ 14 ]. In COVID-19 patients, the prevalence of phantosmia also fluctuates between studies, from 10% [ 15 ] to 34% when OD is still present up to 11 months after the acute phase of the disease [ 11 ]. Second, the underlying mechanisms responsible for phantosmia and other sensory hallucinations are far from being understood, but typically involve peripheral and central causes [ 6 , 16 ]. Third, phantom smells vary widely in their forms from subject to subject [ 16 ]: they may have different durations and frequencies of occurrence, and may be associated or not with other ODs. They are also more often reported by women than by men [ 8 , 16 ], but not always [ 10 ]. Besides, contrary to quantitative ODs that increase with age, experiencing phantom smells was found to be not affected by age [ 17 , 18 ], or even to be more frequent in younger individuals [ 8 , 16 ].
While quantitative ODs can be assessed objectively with psychophysiological methods [ 19 ], the subjectivity of phantom smells invites to study them by letting participants fill in questionnaires about their experiences. This can even be done online, which is particularly convenient when patients cannot be approached, as was the case at the start of the COVID-19 pandemic. Usually, phantom smells are preconceived as negative by the investigators based on past experience with patients [ 8 , 10 , 14 , 16 ]. Instead, in this article we present data obtained from an online questionnaire in which we framed questions about phantom smells in such a way that participants can describe them freely. The diversity of answers obtained with this approach called for an analysis based on Natural Language Processing (NLP), a set of techniques enabling, among other things, to reveal the valence contained in human language [ 20 ].
Given the extent of reported OD following COVID-19 (43% of COVID-19 patients worldwide according to a meta-analysis [ 21 ]) and the millions of cases over the world since the SARS-CoV-2 appeared, it is mathematical that the number of people suffering from phantosmia will increase significantly in the coming months. It is therefore important to characterize this phenomenon in order to provide the most comprehensive descriptive model possible and to better inform patients and practitioners. We further focused on how different individual characteristics could influence phantom smell perception. For instance, women are often found to react more emotionally to odors and are better at identifying odors [ 22 ]. In addition, older adults tend to report fewer emotional experiences (positive or negative) than younger adults [ 23 ]. When describing a smell, older adults also appear to use references to its characteristics more often than to its source [ 24 ]. As phantom smells are often related to something burning, smoking status may also play a role. Finally, all aspects of the associated quantitative OD (type, onset speed, persistence and duration) could impact how the phantosmia is described. With this in mind, our study has four main objectives. Firstly, we determine the prevalence of phantosmia in COVID-19 patients with OD. Secondly, we seek to identify factors modulating this prevalence, including gender, age and smoking status of the participants as well as the characteristics of their OD (type, onset speed, persistence and duration). Thirdly, we refine the study of the dynamics of the occurrence of phantosmia after contracting COVID-19 by comparing different models (linear, quadratic and logarithmic). Fourthly, we investigate the words used in the descriptions of the phantosmia, both quantitatively and qualitatively. In particular, we look at whether the number of keywords used varies between participants and at the variables that influence the valence of the descriptions or the use of certain categories of words.
Participants in an online survey ( https://form.crnl.fr/index.php/146862?lang=fr ) answered questions about their sociodemographic status, their COVID-19 status and their OD status (see details in [ 5 ]) between 8 April 2020 and 20 April 2021. To be included in the analysis, participants had to complete the entire questionnaire for the first time, have been positive for COVID-19 (either via a PCR test or, for participants at the beginning of the pandemic, based on their symptoms as it was a common way to detect COVID-19 due to limited access to PCR tests), and have reported having an OD. For the full inclusion criteria and inclusion tree, see Fig. S1. The final sample consisted of 4691 participants: 3763 women (80.2%) and 928 men (19.8%), with an average age of 40.4 ± 12.5 years-old (mean ± sd). Among them, 1723 were considered to have phantosmia (i.e., their descriptions fitted the definition of phantom smells).
Evaluation of phantosmia
Unlike other studies focusing on phantosmia [ 8 , 14 , 16 , 18 ], we decided to ask an open-ended question with as little guidance as possible. In our opinion, this approach is justified by the fact that phantom smells are inherently a subjective experience. The exact formulation of our question was (originally in French): “In the last few days/weeks, have you had any olfactory hallucinations (phantom smells)?”. If the participants answered "Yes" to this question, they were then given the opportunity to freely describe these phantom smells.
We assessed the prevalence of phantosmia in respondents with OD participating in our study (i.e., number of “yes” answers to the question about phantosmia), as well as the potential effect of seven factors on this frequency (age, gender, smoking status [smoker or non-smoker], OD type [partial/hyposmia or total/anosmia], OD onset speed [progressive or sudden], OD persistence [fluctuating or permanent] and OD duration). As the most prominent and informative effect in terms of dynamics of appearance of phantosmia was OD duration, we further explored the type of function that best fitted this relationship between phantosmia frequency and OD duration by performing a series of regression models (linear [increase or decrease?], quadratic [increase followed by decrease?], logarithmic [increase followed by plateau?]). This analysis was performed over a period of 1 to 60 weeks (i.e., 15 months) of OD duration.
Analysis of qualitative descriptions
We examined the descriptions of the phantom smells and how the seven factors cited above could modulate these descriptions.
First, we calculated the number of different keywords used by each participant to describe their phantom smell(s).
Second, in an attempt to summarize the verbal descriptions, we associated each keyword used by the participants to describe their phantom smells with one or two of the following overarching categories: “characteristic” (i.e., a characteristic of the odor, generally an adjective), “duration” (i.e., how long or how frequent the phantom smell lasts/is), “health” (i.e., health consequences of phantom smells), “location” (i.e., where the phantom smell occurs), “position” (i.e., the body position in which the phantom smell occurs) and “source” (i.e., the source of the odor). The “source” category was further divided into the following subcategories: “detergent” (i.e., toxic products), “fire” (i.e., something burning), “food” (i.e., a food item), “hydrocarbon” (i.e., fuel), “hygiene” (i.e., body hygiene), “tobacco” (i.e., tobacco use) and “others” (all remaining sources). The distribution of usage of each category shows that keywords pointing to the “source” of the phantom smell are the most frequent, followed by keywords describing a “characteristic” of the phantom smell (Fig. S2A). The 3 most common “source” subcategories are “fire”, “food” and “tobacco” (subcategory “others” aside; Fig. S2B). Therefore, we conducted analyses to determine whether these two categories (“source”, “characteristic”) and three subcategories (“fire”, “food”, “tobacco”) varied according to individual factors.
Third, we analyzed the keywords in detail by searching which keywords were more specifically used by particular groups of participants, using the tf-idf (term frequency-inverse document frequency) analysis detailed in the Supplementary Material.
Fourth, we focused on the qualitative content of the descriptions of phantosmia by following a Natural Language Processing approach. This approach allowed us to produce word clouds associated with phantosmia (Figs. S3 and S4), and to conduct a sentiment analysis of the valence (positive or negative) of the descriptions, using the R package sentimentr [ 25 ]. A sentiment analysis requires the mining of the text to be analyzed as well as an independent evaluation of the valence associated with the words used in the text, before combining these two components [ 26 ]. We first retrieved all the different keywords ( N = 623 French keywords) used in the participants’ descriptions of phantom smells. Then, we conducted a new anonymous survey on a different panel of participants ( N = 313 participants). This step was critical because no French lexicon based on the valence associated with odor descriptions was available. Each participant had to report its gender (women: 247 [78.9%] and men: 66 [21.1%]) and age (mean ± sd: 35.5 ± 13.7 years old) and to evaluate 30 keywords in a random order. Each keyword characterizing a phantom smell was evaluated on a valence scale ranging from − 10 (negative odor) to + 10 (positive odor). More details about the valence of the keywords can be found in the Supplementary Material.
The following analyses were performed in R.4.1.1 [ 27 ]. The statistical threshold for significance was set at α = 0.01.
The factors influencing the prevalence of phantosmia were investigated using a logistic regression with the glm() function. The presence (1) or absence (0) of phantosmia was the response variable. The explanatory variables were: (i) age, (ii) gender (men or women), (iii) smoking status (smoker or non-smoker), (iv) OD type (partial [hyposmia] or total [anosmia]), (v) OD onset speed (progressive or sudden), (vi) OD persistence (fluctuating or permanent) and (vii) OD duration. The two numeric variables (age and OD duration) were scaled before the analyses to facilitate the interpretation of the estimates. We conducted backward elimination of non-significant variables until the minimal model containing only significant variables was reached.
Then we limited our analysis to the relationship between OD duration and phantosmia prevalence in order to determine more precisely its nature. Three different models (linear, quadratic and logarithmic) were fitted to the data and their associated Akaike Information Criteria (AIC) were recorded in order to determine which model had the lowest AIC (i.e., provided a better fit to our data).
The factors influencing the number of keywords used in describing phantosmia were investigated using a generalized linear model with a positive-Poisson distribution (as all descriptions had at least one keyword) with the vglm() function from the VGAM package [ 28 ]. The same seven explanatory variables as detailed above were used and non-significant variables were dropped one by one until the minimal model was reached.
The average sentiment score associated with the descriptions of phantosmia (resulting from the previously described sentiment analysis) was investigated using a linear model with the lm() function. Again, the same seven explanatory variables were fitted in the full model and the non-significant variables were removed one by one until the minimal model was reached.
To analyze the categories used to describe phantosmia, we focused on the two main categories, “source” and “characteristic” (because they are representing 90.8% of all categories) and ran a bivariate odds ratio model (i.e., a combination of two logistic regressions in a single model) with the function vglm(). The same model selection procedure as before was followed, starting with the same seven explanatory variables.
For the three subcategories that had enough occurrence to warrant further analysis (“fire”, “food” and “tobacco”), we ran three separate logistic regressions with the same model structure and selection as before.
Prevalence of phantosmia in COVID-19
Following the inclusion criteria (Fig. S1), 4691 respondents to our online questionnaire about ODs were retained and all reported OD. Among these participants, 2016 (43.0%) reported a phantosmia, while 2675 (57.0%) reported other types of OD. Based on a subjective analysis of the description of the reported phantosmia, we considered that 1723 (85.5%) truly described phantom smells (others confounded them with parosmia or their descriptions were too vague to be classified as a phantosmia). In our dataset, the prevalence of phantom smells in participants with COVID-related OD was thus 1723/4691 = 36.7%.
Factors modulating the prevalence of phantosmia
The prevalence of phantosmia was significantly affected by five of our explanatory variables (seven variables were considered: age, gender [man or woman], smoking status [smoker or non-smoker], OD type [partial/hyposmia or total/anosmia], OD onset speed [progressive or sudden], OD persistence [fluctuating or permanent] and OD duration), while two variables were non-significant (Fig. 1 ). Namely, the probability to report phantosmia was higher when OD was fluctuating rather than permanent ( β = 0.75 ± 0.07, z = 11.2, p < 0.0001; OR [99% CI] 2.12 [1.86–2.42]), lasted longer ( β = 0.44 ± 0.03, z = 13.2, p < 0.0001; OR [99% CI] 1.56 [1.46–1.67]), was partial rather than total ( β = 0.39 ± 0.08, z = 4.7, p < 0.0001; OR [99% CI] 1.47 [1.25–1.73]) and appeared progressively rather than suddenly ( β = 0.28 ± 0.09, z = 3.1, p < 0.01; OR [99% CI] 1.32 [1.11–1.58]). Furthermore, women were more likely to report phantosmia than men ( β = 0.48 ± 0.09, z = 5.65, p < 0.0001; OR [99% CI] 1.62 [1.37–1.92]). The predicted probability to report phantosmia for a woman with a partial, fluctuating, long-lasting OD that appeared progressively was 92.9%, whereas the predicted probability to report phantosmia for a man with a total, permanent OD that appeared suddenly and did not last long was 15.4%.
Results from the logistic regression on the probability to report phantosmia ( N = 4691 participants). A Odds-ratios (OR) and 99% confidence intervals of the significant variables in the minimal model. Note that for continuous variables, OR are given for each standard deviation of the corresponding variable. Effects of B gender, C OD type, D OD onset speed, E OD persistence and F OD duration on the probability to report phantosmia. G Prevalence of phantosmia (in blue) as a function of OD duration. In F , circle size is proportional to the number of participants. In B , C , D and E , square size is proportional to the percent of participants reporting phantosmia for each corresponding category, respectively
Dynamics of the appearance of phantosmia in COVID-19
When we examined the relationship between OD duration and the prevalence of phantosmia in a window of about 15 months after OD onset, results showed that the logarithmic function had a better fit to the data (AIC = 5639) than the quadratic (AIC = 5727) or the linear (AIC = 5867) function (Fig. 2 ). The frequency of phantosmia strongly increases during the first 8 weeks of ODs approximately, before reaching a plateau.
Relationship between the prevalence of phantosmia and the OD duration ( N = 4691 participants). For visual clarity, OD duration has been binned per week prior to calculating the corresponding prevalence (the underlying model took into consideration the raw data). Black dots correspond to phantosmia prevalence for each week of OD duration and their size is proportional to the number of participants in this bin. The dotted red line corresponds to the linear relationship, the dashed green line corresponds to the quadratic relationship and the solid blue line [slightly bigger to underline its better fit] corresponds to the logarithmic relationship
Description of phantom smells in COVID-19
Number of descriptors.
The number of keywords used to describe phantosmia was 2.43 (sd: 1.37) on average, and was not affected by any of our explanatory variables at α = 0.01: neither age, gender, smoking status nor any of the OD characteristics impacted the number of keywords used by participants to describe their phantosmia.
When considering which categories of words participants used to describe their phantosmia, we found that most descriptions contained a reference to the source (51.9%; e.g., “smoke”, “cigarette”) or to a characteristic of the smell (41.2%; e.g., “burnt”, “unpleasant”) (Fig. S2A). Regarding how the use of these categories vary as a function of our seven factors of interest, we found that older participants used more frequently keywords referring to the source (in blue in Fig. 3 A, B; β = 0.33 ± 0.06, z = 5.2, p < 0.001; OR [99% CI]: 1.39 [1.23–1.57]) and less frequently keywords describing a characteristic (in red in Fig. 3 A, B; β = −0.23 ± 0.05, z = −4.5, p < 0.001; OR [99% CI] 0.80 [0.72–0.88]). Furthermore, participants with longer OD referred more frequently to a characteristic of their phantom smell (in red in Fig. 3 A, C; β = 0.19 ± 0.05, z = 3.7, p < 0.001; OR [99% CI] 1.21 [1.09–1.34]) and less frequently to its source (in blue in Fig. 3 A, C; β = − 0.27 ± 0.06, z = -4.7, p < 0.001; OR [99% CI] 0.76 [0.68–0.86]).
Results from the bivariate odds ratio model ( N = 1723 participants) on the probability to use a specific keyword category (either source or characteristic, excluding all other rarer categories, see “Methods”). A Odds-ratios (OR) and 99% confidence intervals of the significant variables in the minimal model. Effects of B age and C OD duration on propensity to use a keyword referring to the source (blue lines and shades) or to a characteristic (red lines and shades) of a phantom smell. Lines represent predicted probabilities of logistic regressions and shades represent their 99% confidence intervals
In a finer-grained analysis of the categories, we examined the most frequently cited subcategories of sources, namely “fire”, “food” and “tobacco” (Fig. S2B). None of the seven explanatory variables had an effect on the probability to make references to products or usages linked to “fire” or “food”. However, as for references to the “source” of the phantosmia, we found that older participants ( β = 0.29 ± 0.06, z = 4.6, p < 0.001; OR [99% CI] 1.34 [1.14–1.58]; Fig. 4 A, B) and participants with shorter OD duration ( β = −0.25 ± 0.07, z = − 3.7, p < 0.001; OR [99% CI] 0.78 [0.65–0.92]; Fig. 4 A, E) made more references to “tobacco” to describe their phantom smells. In addition, non-smokers made more references to “tobacco” than smokers ( β = 0.55 ± 0.18, z = 3.1, p < 0.01; OR [99% CI] 1.74 [1.12–2.79]; Fig. 4 A, C). Finally, participants with fluctuating OD made more references to “tobacco” than participants with permanent OD ( β = 0.35 ± 0.13, z = 2.8, p < 0.01; OR [99% CI] 1.42 [1.03–1.98]; Fig. 4 A, D).
Results from the logistic regression on the probability to refer to tobacco to describe phantosmia ( N = 1723 participants). A Odds-ratios (OR) and 99% confidence intervals of the significant variables in the minimal model. Note that for continuous variables, OR are given for each standard deviation of the corresponding variable. Effects of B age, C smoking status, D OD persistence and E OD duration on the probability to refer to tobacco. In B , F , circle size is proportional to the number of participants. In C , D , square size is proportional to the percent of participants referring to tobacco for each corresponding category, respectively
The word cloud illustrating the keywords used to describe phantosmia shows that negatively-connoted keywords are more frequent (Fig. S3), with the most frequent being “burnt” (319 occurrences, 7.63%), “smoke” (208 occurrences, 4.97%) and “cigarette” (205 occurrences, 4.90%). As age and OD duration were found to be prominent factors of variation in the previous analyses by categories, we intended to better characterize the keywords used by younger and older participants, as well as by participants with a shorter and longer OD duration. As an illustration, specific word clouds associated with young vs old and short OD vs long OD can be found in Fig. S4. The tf-idf (term frequency-inverse document frequency) analysis revealed that the 4 keywords most specific of younger participants were: “imagination”, “blood”, “fluctuating” and “stinging”. For older participants, the 4 most specific keywords were: “cigarette smoke”, “chemical”, “grilled bread” and “exhaust pipe”. For participants with shorter OD duration, the 5 most specific keywords were (the last 3 were ex-aequo): “sensation”, “blood”, “bleach”, “chlorine” and “vomit”. Finally, for participants with longer OD duration, the 4 most specific keywords were: “chemical”, “sewer”, “spicy” and “fuel”.
Sentiment analysis (valence of the descriptions)
In accordance with the nature of the keywords illustrated in the word cloud (Fig. S3), the sentiments associated with the descriptions of phantosmia (derived from the evaluation of each keyword’s valence by an independent group of participants, see Methods) were negative for 77.9% of the participants and neutral or positive for the other 22.1% (Fig. 5 ). The average sentiment score associated with the description of phantosmia was influenced by only one of our seven explanatory variables. Participants who had a fluctuating OD described their phantosmia slightly more negatively than participants with permanent OD ( β = 0.05 ± 0.02, z = 2.9, p < 0.01; Fig. S5).
Distribution of sentiments associated with the description of phantosmia (77.9% negative, 22.1% neutral or positive; N = 1723 participants). Each line represents a participant and each dot represents a keyword used by the participant to describe his/her phantosmia (keywords used by the same participant are connected by thin grey lines). The bigger red (negative descriptions) and green (positive descriptions) dots represent the average sentiment score of each participant (participants are sorted based on this average score). The vertical blue line represents a neutral evaluation, while scores between − 1.0 and 0.0 represent negative descriptions and scores between 0.0 and + 1.0 represent positive descriptions. The sentiment value associated with each keyword was determined by an independent sample of participants on a scale from − 10 to + 10 (see “Methods”). The inset on the bottom right represents the density distribution of the average sentiment score of the participants (negative descriptions in red and positive descriptions in green)
COVID-19 has affected many people over the world, often with associated OD. This pandemic therefore represents a unique occasion to study a previously rare, but unfortunately increasing, qualitative OD: phantosmia. By analyzing the responses of more than 4500 individuals, we showed that the prevalence of phantosmia in COVID-19 patients with OD was very high (37% of 4691 people). This prevalence was influenced by the gender of the participants (more frequent in women), and the probability to report phantosmia differed as a function of OD characteristics (higher in fluctuating, long-lasting, partial ODs that progressively settled in). In particular, the prevalence of phantosmia ranged from 14% at the very beginning of the olfactory symptoms of COVID-19 to 56% after 6 months. The dynamics of the prevalence of phantosmia as a function of OD duration is best explained by a logarithmic relationship, with a strong increase at the beginning subsequently followed by a plateau.
The prevalence of phantosmia found in our study was in line with other studies using online questionnaires completed by participants of different countries: up to 34% of COVID-19 patients with OD [ 11 ] and 31% of patients with more varied etiologies of OD [ 29 ], for instance. Such a high percentage may result from a selection bias in our online questionnaire (among other limits of the approach, which are detailed in [ 5 ]). People who are the most affected by their ODs, including persons with phantosmia, may have been more likely to spontaneously participate to our study. However, this high prevalence may also stem from a known association of phantosmia with depression [ 30 ], the global prevalence of which has drastically increased during the pandemic [ 31 ]. The fact that women appeared to be more prone to phantom smells than men confirms some previous findings [ 8 , 16 ], but not all [ 10 ]. Age did not seem to be an influential factor in our study, while higher prevalence of phantosmia have been reported elsewhere in younger participants [ 8 , 16 ].
Of particular interest for the understanding of this olfactory phenomenon are the relationship between its occurrence and OD characteristics. First, evidence is pointing towards the necessity of having an at least partially functioning olfactory system to experience phantom smells. Indeed, we found that phantom smells were more frequently reported when OD appeared progressively than when it appeared suddenly. Phantom smells were more prevalent in hyposmic than in anosmic patients, and in fluctuating (vs. permanent) ODs. Second, as also showed in another group of COVID-19 participants [ 11 ], we found that the prevalence of phantosmia increases as the duration of the smell disorders associated with COVID-19 increases. While there were anecdotal reports of very brief episodes of phantosmia on the day preceding the total loss of smell in a few patients, in most cases phantosmia occurs in a delayed fashion, sometimes even after apparent recovery as this starts to be reported in case studies for other qualitative disorders [ 12 ]. This is consistent with Leopold [ 6 ]’s statement that olfactory distortions (including phantosmia) seem to occur either during olfactory receptor neuron death or regeneration. It is noteworthy that COVID-19 patients experiencing phantosmia often have an ability to smell (quantitatively) within the normal range (6 patients out of 9 with phantosmia were normosmic while the others were hyposmic in [ 9 ] and patients with phantosmia and/or parosmia did not differ in Sniffin’ Sticks test scores from patients without qualitative ODs in [ 32 ]).
Although studies are clearly needed to better characterize the pathophysiology of phantosmia, several hypotheses about peripheral and central mechanisms (which are not necessarily exclusive) of such a phenomenon have been formulated. At the peripheral level, lower number of olfactory neurons in the olfactory epithelium, higher number of immature neurons and disordered growth of olfactory axons have been found in patients with phantosmia [ 6 ]. Peripheral phantosmia is more often intermittent and worse on one side, relieved by nasal obstruction and anesthesia/resection of the olfactory epithelium [ 33 ]. Some reports in our study indicated that mechanical actions affecting the nasal cavity, such as yawning or blowing one’s nose, could trigger a phantom smell [ 5 ]. Central mechanisms may also occur, with manifestations that are constant, bilateral and not relieved by any of the options mentioned previously [ 33 ]. This is consistent with abnormally high brain activity in several frontal, insular and temporal regions [ 6 ], but also with some etiologies of phantosmia outside COVID-19 (psychiatric diseases, neurologic and neurodegenerative disorders). Consistent with the central hypothesis, the reports of several patients in our study were in favor of an effect of suggestion (like reading/talking about a smell, which would trigger the phantom smell) and of attention (phantosmia being more present during the peak periods of the epidemic waves, or disappearing during a limited period in which the patient has changed environment and directed her attention to a person to help). Representation of an odor can be elicited in people without pathological condition (imagined odor: [ 34 ]). Possible dysfunction or damage in the central olfactory pathways (olfactory bulb, olfactory tract and/or primary/secondary cortices) [ 33 ] could trigger such representations. It has been suggested that disinhibition of olfactory excitation could originate in these unwanted odor perceptions.
The shape of the prevalence curve (Fig. 2 ) suggests that there might be both peripheral and central phenomena in play. The prevalence of phantosmia reaches a plateau at a time (about 8 weeks) were neuronal regeneration in the olfactory epithelium is likely to take place: indeed, regeneration time of a healthy epithelium after axotomy (including olfactory bulb reinnervation) is about 30 days in mammals [ 35 , 36 ], but could be longer in a damaged epithelium. From this time on, the prevalence curve then illustrates what seems to be a rather installed phenomenon, since it does not decrease over 60 weeks after the beginning of the first COVID-19-related OD. This is particularly preoccupying first because, whereas parosmia seems to be a positive sign of recovery, phantosmia appears to be a poorer predictor of recovery in the most recent studies in COVID-19 patients [ 37 ] as well as in patients with varied etiologies [ 38 ] (but see [ 39 ] for contradictory findings that occurrence of parosmia or phantosmia has little prognostic value). And second, because to date there is not enough evidence in the literature to formulate treatment recommendations for phantosmia (or parosmia): only anecdotal evidence can be found for the local use of some medical therapies, such as antimigraines, antipsychotics or antiepileptic, with success rates depending on the patients’ etiology [ 33 ] (see also the recent study by [ 40 ] for an encouraging effect of intranasal sodium citrate in reducing phantosmia).
Additionally, with regards to the qualitative description of phantom smells, we found that 78% of the participants described their phantosmia as a negative experience, and this was more marked when the OD was fluctuating. Why phantom smells are more often unpleasant is an intriguing question, to which we can propose several possible answers. First, one of the main functions of olfaction, which has the most immediate consequences for survival, is the detection of threats. One can thus hypothesize that, (i) in the case of anarchic activation of olfactory neurons and (ii) assuming there is a central contribution to the generated olfactory percept, olfactory representations that are preferentially generated are those of odors that are the most relevant for survival (smoke, decay/fermentation…). The fact that the odor of a toxic substance, tobacco, was cited more often by non-smokers as a phantom smell is totally in line with this, given that the threatening value of tobacco products is likely to be stronger in this subgroup. Second, the dimensions of unexpectedness (phantom smells occurring in a non-predictable manner) and incongruency (phantom smells unrelated with the actual physical environment) may contribute significantly to the unpleasantness of this experience since they are significant determinants of the responses to smells [ 41 ]. Finally, fluctuation of the occurrence of phantom smells is likely to worsen the deleterious effect of unexpectedness, explaining why fluctuating OD is a significant predictor of negativity of phantosmia.
Another result of interest is that participants with OD of shorter duration and older participants tended to favor source names (i.e., descriptions of the olfactory experience). Conversely, participants with OD of longer duration and younger participants referred more to odor characteristics (i.e., more emotional descriptions of the olfactory experience). The fact that older participants used more words linked to the potential source of the phantom smell than to its characteristics contrasts with previous results [ 24 ], which found the opposite pattern when participants were asked to describe an actually perceived odorant. It could therefore be that semantic usage differs with age depending on whether participants have to describe a real or a mental construction of a smell. In addition, as elderly persons are typically less sensitive to emotions [ 23 ], it could be that older participants use less emotional descriptors and thus refer more to the source of the smell. The different usage of semantic categories with age may be linked to age-related changes in word representation and retrieval [ 42 ]. Regarding the effect of OD duration, it is possible that people with longer OD are more annoyed by the phantom phenomenon and use more adjectives to describe how they feel about it whereas people with shorter OD are still in the exploratory phase where they have a more analytical approach, trying to define what the odor is exactly. More broadly, it is worth mentioning that phantosmia is subjective and may be affected by the usage of a specific language. Future studies could therefore try to assess how phantom smells are described by respondents from different cultures and/or languages with different sizes of smell-related vocabularies [ 43 ].
Finally, we would like to stress the importance of studying phantosmia separately from parosmia. These qualitative ODs are often grouped together in the literature, but it has been suggested that this may be a mistake since they have different patterns of expression depending on demographic factors, etiologies and consequences on the quality of life [ 10 ]. Although adopting a questionnaire approach has limitations [ 5 ], it provides useful quantitative and qualitative elements to gain additional insights into previously rarely observed phenomena such as phantosmia. Future studies are needed to better understand this category of sensory hallucinations and its physiopathology. As well as parosmia, phantosmia has very deleterious consequences on the patients’ quality of life [ 44 ]. In spite of this, knowledge of these and other related ODs remains low amongst medical professionals [ 5 , 45 ] and the medical community is still lacking therapeutic options [ 29 ]. Hopefully, the number of studies on phantosmia, which already significantly increased in 2020 and 2021, will continue to grow in the future to better answer the needs of the many patients suffering from this long-term sequalae of COVID-19.
Conclusion on clinical relevance
By using a model of viral infection often associated with olfactory disorders, COVID-19, we pointed at the high frequency of the under-studied phenomenon of phantom smells in patients with post-infectious ODs. Indeed, using spontaneous reports of patients with an online questionnaire, we found that 37% of post-COVID patients with ODs experienced phantom smells. It is important to note that this figure is likely to overestimate the prevalence of this symptom on the ground, since people who suffer from their OD may be over-represented within the sample of volunteers who answered the online questionnaire. It may though be in line with the frequency observed by the clinicians because patients who decide to consult for their phantosmia are those who are adversely affected by their condition. The characteristics of phantom smells (i.e., which smells, (un)pleasantness of the smells) and their dynamics of occurrence after OD onset, as we report them in this article, are certainly well representative of the reality on the ground. To better inform patients, clinicians’ attention should be drawn to the factors associated with a higher probability to develop phantosmia, namely being a woman and displaying a fluctuating/long-lasting/progressively installed OD. Finally, it must be kept in mind by the medical and scientific community that research on the characteristics, mechanisms and remediation of phantosmia is dependent on patients’ verbal reports, since there is no objective way to measure sensory hallucinations.
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The authors wish to thank all the people who helped disseminate the questionnaire. This work was carried out with the financial support of the IDEXLYON Project of the University of Lyon as part of the Future Investments Program (ANR-16-IDEX-0005, CORODORAT project to CF and MB).
Christophe Bousquet and Kamar Bouchoucha: co-first authors.
Moustafa Bensafi and Camille Ferdenzi: co-last authors.
Authors and Affiliations
Lyon Neuroscience Research Center, CNRS UMR5292, INSERM U1028, University Claude Bernard Lyon 1, CH Le Vinatier, Bât. 462 Neurocampus, 95 boulevard Pinel, 69675, Bron Cedex, France
Christophe Bousquet, Kamar Bouchoucha, Moustafa Bensafi & Camille Ferdenzi
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Conceived and designed the study: MB, CF. Wrote the paper: CB, MB, CF. Data acquisition and curation: CB, KB, MB, CF. Performed analysis: CB, KB. Edited and approved the final manuscript: CB, KB, MB, CF.
Correspondence to Moustafa Bensafi or Camille Ferdenzi .
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Bousquet, C., Bouchoucha, K., Bensafi, M. et al. Phantom smells: a prevalent COVID-19 symptom that progressively sets in. Eur Arch Otorhinolaryngol 280 , 1219–1229 (2023). https://doi.org/10.1007/s00405-022-07649-4
Received : 27 May 2022
Accepted : 06 September 2022
Published : 29 September 2022
Issue Date : March 2023
DOI : https://doi.org/10.1007/s00405-022-07649-4
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Phantosmia with COVID-19 Related Olfactory Dysfunction: Report of Nine Case
1 Otolaryngology-Head and Neck Surgery Clinic, Nusaybin State Hospital, Adar Street, 10/A-10 , Nusaybin, Mardin Turkey
Mustafa Koray Balcı
2 Otolaryngology-Head and Neck Surgery Clinic, Atatürk Training and Research Hospital, Katip Celebi University, İzmir, Turkey
Phantosmia has been described as a sense of smell without a true stimulating odor and not been reported with COVID-19 disease. Nine patients admitted to Ear Nose Throat (ENT) Clinic with complaints of a phantom smell sense after an average of 33.5 ± 9.5 days after the initial PCR diagnosis. According to the Sniffin 'Sticks test, phantosmia was associated with objective hyposmia in three patients with the persistent phantom smell, and other six patients were detected normosmic. Phantosmia or olfactory hallucinations have not been previously associated with COVID-19 disease. Additionally, COVID-19 related phantosmia showed different characteristics according to described in the literature.
The online version contains supplementary material available at 10.1007/s12070-021-02505-z.
Phantosmia has been described as a sense of smell without a true stimulating odor and is a subjective olfactory dysfunction. Olfactory hallucinations have been previously associated with migraine typed headaches, endoscopic skull base surgery, intracranial tumors, brain radiotherapy treatment, and head trauma in the literature [ 1 ]. As described in the literature, phantosmia can persist for years. Olfactory dysfunction is one of the preliminary symptoms of COVID-19 disease, and it can occur as hyposmia, anosmia, or and sudden loss of smell [ 2 ]. However, COVID-19 related phantosmia or olfactory hallucination has not been reported in the literature before. In this report, nine confirmed COVID-19 patients with olfactory hallucinations were presented.
The demographic and clinical characteristics of the patients are summarized in Table Table1. 1 . All of the patients admitted to Ear Nose Throat (ENT) Clinic at second referential state hospital with complaints of a phantom smell sense after an average of 33.5 ± 9.5 days after the initial PCR diagnosis. All patients had completed COVID-19 treatment and emerged from isolation. The main symptoms of the patients were fever, cough, and weakness at the initial diagnosis. Three patients had Sars-Cov-2 related thorax Computed Tomography (CT) findings. All patients confirmed for COVID-19 disease with PCR test by nasopharyngeal swabs. Aura-like phantom odor sensation noticed by three patients during two or three days of the disease when symptoms were most severe and then disappeared. Two patients reported that the phantom smell sense continued during the disease but the onset of phantom smell was not distinguished. Four (44.4%) patients still complained of phantom odor during ENT admission. According to the Sniffin' Sticks test, phantosmia was associated with objective hyposmia in three (33.3%) patients with the persistent phantom smell (TDI score between 15.5 and 30.5; odor threshold, odor discrimination, and odor identification).
The demographic and clinical characteristics of the patients
TDI odor threshold, odor discrimination, and odor identification, m minutes, w week,
Medical treatment included hydroxychloroquine (200 mg bid for 5 days), moxifloxacin (400 mg once daily for 7 days), favipiravir (Day 1: 1600 mg bid for the first day; 600 mg bid 2–5 days), enoxaparin (40–60 mg/d), dexamethasone (20 mg/d for first 3 days, then 4 mg/d) for all patients. During the disease, only a mild C-reactive protein (CRP) elevation was present in three (33.3%) patients (Table (Table1). 1 ). In eight (88.8%) patients, the PCR test turned negative 1 week after the initiation of treatment, while PCR became negative at the 4th week for a 32-year-old male patient. Interestingly, in this patient, only dizziness continued for 40 days. In the ENT examination of the patients, septum deviation, concha hypertrophy, discharge, mucosal dryness, congestion, or nasal polyp were not detected. In addition, none of these patients had ever experienced phantosmia before. None of the patients had a history of chronic disease, chronic drug use, maxillofacial trauma, or surgery. The follow-up period was 60.4 ± 23.0 days after first ENT admission. Brain Magnetic Resonance Imaging (MRI) was performed for all patients and no pathology was found (Fig. 1 ). While only observation recommended for three patient with persistent phantosmia, carbamazepine (400 mg daily, p.o.) was prescribed to one patient who had difficulty eating because of nausea due to dirt smell sensation. Two months after the carbamazepine treatment, the patient reported that she could tolerate dirt smell, but her phantom sense of smell did not disappear.
30-year-old female patient, T1-weighted axial MRI image from the level of olfactory fossa
Hyposmia, anosmia, or sudden onset of anosmia were shown significant symptoms for asymptomatic or mild COVID-19 disease although the mechanism of the olfactory dysfunction was not understood [ 3 ]. Phantosmia was classified as a qualitative disturbance of smell function and during the COVID-19 pandemic, this phenomenon was not reported. Phantosmia occurs due to a number of etiologies, including chronic rhinosinusitis, cranial trauma, intracranial hemorrhage, epilepsy, psychiatric conditions, brain radiotherapy, neurologic disorders, iatrogenic causes, and neurologic and neurodegenerative disorders and conductive or sensorineural pathophysiology of this specific symptom is still unclear [ 1 ]. The frequency of phantosmia has been reported by up to 25% in patients with odor disorder, and the incidence is higher in the elderly compared to the young population [ 3 ]. Sjölund et al. [ 4 ] reported that phantom smells were experienced less than once a month (54%) and the most frequently reported phantom smell was smoky or burnt (46%) in a population-based study. In addition, in this study, it was reported that only 17% of patients with a phantom sense of smell had this entity for less than a year. Long-term phantosmia impairs quality of life so, medical, surgical, and olfactory training as treatment options have been reported in current literature [ 5 ].
Gender distribution of the patient similar to reported literature, but despite the increasing frequency of phantosmia with age, all of the patients presented were in the young age group (< 40 y/o). All patients in this study had not previously noted olfactory disturbance or phantosmia. Five of nine (55.5%) patient has not experienced olfactory hallucination again after their symptoms of COVID-19 has regressed. In addition, three patients reported that the phantom smell sensation very obvious at the most severe period of COVID-19 symptoms. Interestingly, five (55.5%) patients had no complaints of anosmia or hyposmia during COVID-19 disease, but hyposmia with phantosmia was detected in a female patient on ENT admission (TDI score: 25.8). While phantosmia persisted in four (44.4%) patients, the sense of phantom smell disappeared in five (55.5%) patients with recovery from COVID-19 disease. Although follow without any treatment was recommended for all patients, a patient with persisted phantosmia requested medical treatment because of the unbearable dirty smell. Monthly control was recommended for all patients with persistent phantosmia. The patient with carbamazepine treatment reported that the sensation of dirty smell decreased in the second month of the follow-up and the treatment was stopped. The request for treatment of the patient disappeared in the 3rd month of follow-up.
Phantosmia or olfactory hallucinations have not been previously associated with COVID-19 disease, however, the development of phantosmia due to olfactory dysfunction is a predictable situation. Although the pathological mechanism is unclear, phantosmia emerged with COVID-19 infection and disappeared after the disease recovery. Although the short follow-up period, this case report showed the presence of a new unusual symptom with COVID-19-associated odor dysfunction.
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No funding was received for this study.
The authors declare that they have no conflict of interest.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Some COVID-19 survivors are experiencing phantom foul smells after recovery
Experts first recognized anosmia, or the loss of smell, as a common symptom of COVID-19 in late March . But for an increasing number of survivors, that reaction is simply the precursor to another more excruciating phenomenon — one in which the region of brain responsible for identifying smell fails to properly rebound — resulting in either distorted smells ( parosmia ) or phantom smells ( phantosmia ).
In a more than 800-person phantosmia support group on Facebook, COVID-19 survivors have begun sharing what they describe as a “depressing” battle with smells. “It has been three months since I recovered from COVID-19. Had multiple symptoms including loss of smell and taste. But a few days ago, I kept smelling burnt toast,” writes Cheryl Marais. “The past two days there is a permanent smell of gasoline.”
A separate, private Facebook group titled “COVID parosmia/anosmia support group” boasts almost 5,000 members. In interviews with Yahoo Life, more than 20 COVID-19 patients from a support group called Survivor Corps described distorted smells — such as peanut butter smelling like mold — as well as phantom smells — such as dog poop in the house of a survivor who doesn’t have a canine.
The Mayo Clinic defines phantosmia as “an olfactory hallucination [that] makes you detect smells that aren't really present in your environment,” and parosmia as when a “smell that's present in your environment is distorted.” Both seem to be linked to damage to the olfactory system, and can happen in the wake of things like sinus infections and other respiratory illnesses. Scientists still aren’t sure exactly why.
Related: University researchers create ‘smell test' for coronavirus infection
Dr. Masha Niv, associate professor of chemical senses and molecular recognition at the Hebrew University of Jerusalem, has been studying the effect of COVID-19 on smell since March. In a study of more than 4,000 patients with smell changes, she says seven percent reported distorted smells and six percent reported phantom smells. Her results, published by the Oxford University Press this summer, suggested that both were caused by COVID-19 — and may be linked to patients’ previous loss of smell.
“Phantosmia does seem to happen following [loss of smell] that is due to other viral infections. So it isn’t surprising,” Niv tells Yahoo Life. “But the numbers are large — because COVID is so prevalent, and because anosmia is much more common in COVID compared to other respiratory illnesses.”
Claire Hopkins, a professor of rhinology at King’s College London who authored the first study on smell loss, says she has seen an increase in the number of patients with these issues. “We have just had a paper accepted for rhinology which shows 45 percent of a cohort who reported COVID loss of smell report parosmia or phantosmia within six months,” Hopkins tells Yahoo Life.
Hopkins says the change typically occurs two to three months after infection, which aligns with stories that were shared with Yahoo Life. In some cases, phantosmia seems to be fairly benign, with one survivor telling Yahoo Life that her phantom smells are “floral” in nature. Another, Jessica Bullock, says the phantom smells she experiences seem to revolve around a condiment. “Every day, multiple times a day I smell ketchup and there’s NO ketchup around,” says Bullock, a 47-year-old in Minneapolis who was diagnosed with COVID-19 in May.
But, for reasons unclear to the rhinology world, many phantom smells and distorted smells are extremely foul in nature. “For months after getting sick with COVID, I kept smelling a rotting meat or dead body smell that would come and go,” says Valarie Kenworthy, a Survivor Corps member who contracted COVID-19 in March. “I seemingly was subconsciously smelling it even in my sleep; because I had the most horrific, graphic, grotesque nightmares I've ever had.”
Parosmia can be similarly unpleasant. “I frequently smell distorted smells. The most recent was shortly after my husband mowed the yard. It should’ve smelled like freshly cut grass; I smelled a sewer leak,” says Tammy Claeson, a 49-year-old teacher in Garland, Texas, who was diagnosed with COVID-19 in July. “I get the phantom gas and sulfur smells, as well.”
Denise Tamir, a lieutenant with the NYPD, says she lost her sense of smell and taste “completely for about three to four weeks,” then experienced distorted smells when it returned. “I started smelling smoke all the time. I didn’t know where it was coming from,” Tamir tells Yahoo Life. “Another two months after that, I started smelling chemicals and my food also started tasting like chemicals. Certain smells that used to smell so nice now smell like something rotten. My laundry detergent, shampoo, conditioner, perfume — all now smell so disgusting to me.”
Hopkins says that symptoms like this are likely a sign that the brain has not fully recovered, leading to error messages in the olfactory region. But while it’s extremely uncomfortable for those experiencing it, Hopkins says the changes could ultimately be a good thing. “It appears to be related to a stage in recovery after smell loss, and so is a positive sign in long term recovery,” Hopkins says. “On non-COVID studies, phantosmia has an average duration of 12 months from time of infection but we are seeing encouraging reports of it resolving in patients around 8-9 months after COVID infection.”
For the latest coronavirus news and updates , follow along at https://news.yahoo.com/coronavirus . According to experts, people over 60 and those who are immunocompromised continue to be the most at risk. If you have questions, please reference the CDC ’s and WHO’s resource guides.
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A Change in Smell After COVID-19 Infection: What You Need to Know
Being able to taste and smell are essential parts of enjoying everyday life. But for some COVID-19 long haulers , these senses can become extremely unpleasant. Some people experience a change to their taste and smell following COVID-19 infection, also known as parosmia (abnormal sense of smell), hyposmia (decreased sense of smell), and anosmia (loss of sense of smell). The good news is it's usually only temporary—in most cases. However, no matter how long these conditions last, it can be very disruptive.
Kristine Smith, MD , a rhinologist and assistant professor in the Division of Otolaryngology (Head and Neck Surgery) at University of Utah Health, answers eight questions about parosmia.
How is parosmia associated with COVID-19?
While it's not known exactly what triggers parosmia , smell disruption can be caused by viral illnesses such as the common cold or influenza. Head trauma, medications, and neurologic diseases such as Parkinson's and other neurodegenerative diseases can also cause parosmia. During a viral illness, the nerve receptors in your nose can be damaged and change your perception of smell. It's believed this same phenomenon occurs during COVID-19 infection.
How are COVID-19 long haulers experiencing parosmia?
A loss of taste and smell is a common symptom of COVID-19 infection. In the recovery phase of COVID-19, a patient normally regains their senses back. However, some people experience a change to their sense of smell about three to four months following infection. People report certain things—like food or body odor—smelling like garbage, rotten eggs, or chemicals. This altered sense of smell is called parosmia.
How common is parosmia?
The number of patients who experience a loss of smell and taste during or after COVID-19 infection ranged widely. The loss or change of taste and smell during COVID-19 infection impacts about 50-75 percent of people. About 25-75 percent go on to develop parosmia in the recovery phase of COVID-19.
When will I get my sense of smell and taste back?
Patients usually improve slowly with time. About 65 percent of people with COVID-19-induced parosmia or hyposmia regain these senses by about 18 months, while 80-90 percent regain these senses by two years.
Who is more likely to develop parosmia?
If you lose your sense of smell or have a reduction in your sense of smell while you have COVID-19, you are more likely to develop a disturbance in your sense of smell later. But you can still experience parosmia even if you didn't originally have smell loss. Patients who are younger and female also seem to have a higher incidence of experiencing post-COVID-19 smell disruption. It's unclear why these groups are more impacted.
Are people still experiencing parosmia with different COVID-19 variants?
The number of people reporting parosmia seems to be changing with COVID-19 variants over time. More cases of parosmia were reported at the beginning of the pandemic with the original SARS-CoV-2 virus. While patients are still experiencing parosmia, the number of patients seeking help with their symptoms is less with the newer variants.
Can parosmia be treated?
There are no guaranteed treatments for post-COVID-19 parosmia. However, some therapies may help some patients. These include:
- Olfactory retraining is the process of retraining your nose to smell . It involves smelling strong scents (citrus, cloves, eucalyptus) every day while thinking about what they smell like to try to help reform normal responses to your nose and brain. Research has shown it can improve parosmia in long COVID patients. It often takes about 6 to 12 weeks to notice an impact and up to 24 weeks for maximal impact.
- Intranasal steroids (fluticasone or mometasone) are low-risk nasal spray therapies. Studies have shown that these therapies can improve sense of smell in about 10-25 percent of patients.
- High-volume saline irrigations or sinus rinses (Neilmed, Netipot, Navage) help improve inflammation in the nose after an infection and may improve recovery after infection.
- Neuromodulating medications alter the way nerve cells send signals. Limited research has shown some improvements in olfactory dysfunction. These medications, such as gabapentin and amitriptyline, are also used to control chronic pain or headaches. Due to side effects, they are mostly used in patients with severe symptoms.
- Eating simpler or bland meals: The more complex the aroma, the more likely it seems to trigger parosmia.
- Eating food cold or at room temperature: Steam is what carries that sense of smell to your nose, which can trigger parosmia.
Other therapies like stellate ganglion blocks , alpha-lipoic acid , and plasma-rich plasma (PRP) injection are being investigated as potential treatments for COVID-induced parosmia. The risks or potential benefits are not yet known.
Home or natural therapies are becoming increasingly common, but DO NOT try these without talking to your doctor first. What you put in your nose could be absorbed in your bloodstream, which could potentially be dangerous to your health.
Can parosmia be dangerous to your health?
Losing your sense of smell or having a change in your sense of smell is not going to directly cause you harm, but it can increase your risk of some potentially harmful things, such as:
- Food poisoning : When your sense of smell comes back wrong or is decreased long-term, it can put you at risk of experiencing food poisoning because you may not be able to tell when something in your fridge has gone bad. People with parosmia should pay attention to expiration dates and labeling leftovers.
- Smoke or natural gas : A person with parosmia may not be able to detect smoke or natural gas in their home. It's important to ensure you have up-to-date smoke and natural gas detectors in your home. If you have a natural gas stove, you may want to consider getting a handheld natural gas detector.
- Mental health : The ability to smell and enjoy food is really important to our well-being. These types of alterations can significantly impact someone's quality of life. Having persistent parosmia can potentially increase the risk for anxiety and depression. It's important to seek help to treat those associated issues.
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COVID: a distorted sense of smell is dangerous but treatable
Professor of Rhinology and Olfactology, University of East Anglia
Carl Philpott receives funding from the National Institute of Health Research. He is affiliated with Fifth Sense.
University of East Anglia provides funding as a member of The Conversation UK.
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Lucy, a patient of mine, contracted COVID-19 in the first wave of the pandemic, before lockdown. She had trouble breathing and her doctor told her to call an ambulance if her lips turned blue. Luckily, she recovered well at home with rest and paracetamol – but it wasn’t the end. A week later, she suddenly lost her sense of smell and taste, which at the time wasn’t a recognised COVID symptom .
Slowly, over the following two months, her sense of smell partially returned. She danced around the kitchen with joy each time she could smell a new aroma. But then, at the end of May, she sat down to breakfast, had a mouthful of egg and nearly threw up. Lucy had developed parosmia, a condition where perceptions of odour are distorted.
Lucy’s triggers included coffee, wine, beer, chocolate, meat, eggs, onions, garlic and lemons. There was no logic to it. One day, something was fine, the next it was rank. A lot of food ended up in the bin; she was hungry and upset.
The smell of trigger foods was otherworldly: somewhere between the smell of death and sewage. It was so intense and offensive, and it lingered for hours. Even attempting to freshen her mouth was fraught as toothpaste was itself a trigger. Eight months on and she has a long list of safe foods that she tries to stick to, such as cheese. Flavour-free toothpaste helps, as does disguising the flavour of some distorted foods with cinnamon or black pepper.
For Lucy, eating remains an anxious experience and she describes mealtimes as boring. Consequently, her diet is unhealthy, her mood is low and relationships are strained . Now and then there is a slight improvement and the blacklisted foods get tried. Occasionally, they are back to normal and she celebrates each little victory. These changes are encouraging her on the road to recovery, even if progress is slow.
Lucy’s experience is very much in keeping with other parosmia sufferers posting similar stories of horror online.
Parosmia is a common smell disorder. It has been linked to viral infections and usually begins after the patient appears to have recovered from the infection.
The fact it is popping up as a delayed symptom in COVID-19 does not surprise olfactologists (smell doctors) who are used to seeing patients with these problems. When viruses cause lasting problems with the sense of smell (post-viral olfactory dysfunction), it is probably because the infection has caused damage to the smell receptor nerves, making them unable to detect the smell molecules that dissolve in the nasal mucus .
Parosmia is believed to occur due to partial recovery of the smell receptors in the top of the nose. Because we recognise smells as mixtures of odour molecules, if some receptors aren’t working, the pattern recognition is affected, and this leads to a distorted signal, which more often is interpreted as unpleasant (troposmia), but can sometimes be a pleasant distortion (euosmia). Nonetheless, the symptom of parosmia is seen by olfactologists as an encouraging sign , even though sufferers find it very hard to contend with.
Retraining your nose
Smell training is a key activity to help overcome the problems of post-viral smell disorders. Not everyone finds it easy, though, so other self-help measures include other forms of nasal stimulation, such as sniffing horseradish or mustard, which activate the trigeminal nerve.
People experiencing parosmia should not suffer in silence. While this is not an area where there is a wealth of evidence to support treatment, olfactologists are used to dealing with these symptoms (including phantosmia) and will sometimes be able to suggest medical treatment that may help to moderate the symptoms . But it is clear that more needs to be done to establish evidence-based treatments for these disabling symptoms and a consultation is underway to boost research in this area .
People suffering from parosmia can get support and advice from Fifth Sense , a charity set up to help people affected by smell and taste-related disorders.
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Unusual COVID-19 symptoms: What are they?
What are some of the unusual symptoms of covid-19.
Coronavirus disease 2019 ( COVID-19 ) can cause a wide range of signs and symptoms. The most common are fever, cough and tiredness.
Other symptoms include:
- Shortness of breath or difficulty breathing
- Muscle aches
- Sore throat
But COVID-19 can cause symptoms you may not expect, including:
- Digestive symptoms. COVID-19 might cause nausea, vomiting or diarrhea — either alone or with other COVID-19 symptoms. Digestive symptoms sometimes develop before a fever and respiratory symptoms.
- Loss of smell or taste. A new loss of smell or taste — without a stuffy nose — is a common early symptom of COVID-19 . Research suggests that most changes in smell and taste often resolve in 30 days. In some people, however, moderate to severe changes in smell and taste can last 60 days or more.
Skin changes. The most common skin changes linked with mild to severe COVID-19 include a flat rash covered with small bumps, discolored areas on the fingers and toes (COVID toes), and hives.
COVID toes appear to be more common in children and young adults. Swelling or discoloration can develop on one or several toes or fingers. The hands, wrists or ankles also can be affected. Blisters, itchiness, rough skin, or painful bumps can occur. A small amount of pus might develop under the skin. The symptoms can last 10 to 14 days or for months.
However, swollen, discolored fingers or toes could also be chilblains, an inflammatory skin condition. Chilblains develop in response to repeated exposure to cold air.
- Confusion. Severe confusion (delirium) might be the main or only symptom of COVID-19 in older people. This COVID-19 symptom is linked with a high risk of poor outcomes, including death.
- Eye problems. Pink eye (conjunctivitis) can be a COVID-19 symptom. Research suggests that the most common eye problems linked to COVID-19 are light sensitivity, sore eyes and itchy eyes.
Signs and symptoms of COVID-19 may appear 2 to 14 days after exposure. They can range from mild to severe. If you think you might be experiencing symptoms of COVID-19 , call your health care provider.
Daniel C. DeSimone, M.D.
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- Menni C, et al. Real-time tracking of self-reported symptoms to predict potential COVID-19. Nature Medicine. 2020; doi:10.1038/s41591-020-0916-2.
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- Pardhan S, et al. Sore eyes as the most significant ocular symptom experienced by people with COVID-19: A comparison between pre COVID-19 and during COVID-19 states. BMJ Open Ophthalmology. 2020; doi:10.1136/bmjophth-2020-000632.
- Kennedy M, et al. Delirium in older patients with COVID-19 presenting to the emergency department. JAMA Network Open. 2020; doi:10.1001/jamanetworkopen.2020.29540.
- Herman A, et al. Evaluation of chilblains as manifestation of the COVID-19 pandemic. JAMA Dermatology. 2020; doi:10.1001/jamadermatol.2020.2368.
- Vaira LA, et al. Smell and taste recovery in coronavirus disease 2019 patients: A 60-day objective and prospective study. The Journal of Laryngology and Otology. 2020; doi:10.1017/S0022215120001826.
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Unique Imaging Findings of Neurologic Phantosmia Following Pfizer-BioNtech COVID-19 Vaccination: A Case Report
- 1 Department of Radiology, North Shore University Hospital-Long Island Jewish Radiology Residency, Zucker Hofstra School of Medicine, Northwell Health, Manhasset, NY.
- 2 Feinstein Institutes for Medical Research, Institute of Molecular Medicine, Northwell Health, Manhasset, NY.
- 3 Department of Radiology, Northwell Health, Zucker Hofstra School of Medicine at Northwell, North Shore University Hospital, Manhasset, NY.
- PMID: 34096896
- DOI: 10.1097/RMR.0000000000000287
Olfactory dysfunction related to SARS-CoV-2 infection and COVID-19 disease is now well established in the literature. In December 2020, the FDA approved the Pfizer-BioNTech and Moderna vaccines for use in preventing COVID-19 in the United States. To the best of our knowledge, this is the first report of a phantosmia post-Pfizer COVID-19 vaccination, with positive magnetic resonance imaging radiographic findings in a patient with documented absence of infection by SARS-CoV-2 virus or concomitant sinonasal disease.
Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.
- Case Reports
- COVID-19 Vaccines / adverse effects*
- Hallucinations / diagnostic imaging*
- Hallucinations / etiology*
- Magnetic Resonance Imaging
- Olfaction Disorders / diagnostic imaging*
- Olfaction Disorders / etiology*
- COVID-19 Vaccines
Everything we know about long COVID, from strange phantom smells to chronic fatigue
People describe lungs that feel packed in flour and brain fog that feels more like dementia. Some experts have warned long COVID is the next 'looming catastrophe'
At first, there was no sense of smell, “zero, zilch, nothing,” for weeks on end.
And then Manali Mukherjee suddenly could smell smoke. She’d find herself in a panic: Is something burning? Is there a short circuit in the house? Some days it was like being inside a smokers’ lounge, the heavy cigarette smell lasting seven or eight hours and causing crippling cluster headaches.
Everything we know about long COVID, from strange phantom smells to chronic fatigue Back to video
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Except there was no smoke at all.
Phantosmia causes people to smell phantom odours, to essentially hallucinate smells, while with parosmia, a known smell is no longer the same. Once-pleasing food can smell unusually unpleasant, like rotting meat.
Mukherjee was diagnosed with COVID-19 in January. In addition to serious olfactory dysfunction, the assistant professor in McMaster University’s department of medicine still has trouble with staggering fatigue, sudden plummeting blood pressure and difficulty focusing. “There were good weeks, and then bad weeks. I just kept thinking, ‘I’m a trained immunologist, I know what might be happening to me, and I’m getting this anxious. What’s happening to other people who don’t know about it?’”
What happened to Mukherjee was long COVID, the same syndrome she’s been granted $500,000 in federal funding to study. It’s a vague, poorly defined condition without a prognosis or proven treatments and that an unclear number of Canadians may have had or may still be living with.
I’m a trained immunologist, I know what might be happening to me, and I’m getting this anxious
People describe lungs that feel packed in flour, brain fog that feels more like dementia and fatigue unlike anything they’ve ever experienced.
Mukherjee believes the answer to these symptoms is rooted somewhere in the immune system, and a hyper-stimulated one: once the virus is cleared, the body’s immune activation goes rogue, unleashing auto-antibodies that turn on its own tissues and proteins. Somehow the immune system has become confused and rowdy, “and what you’re left with is the collateral damage,” Mukherjee said.
With 271 million confirmed infections worldwide, some researchers have warned long COVID is the next “looming catastrophe,” with prevalence estimates all over the map, from as low as two per cent of the COVID “recovered” to as high as 89 per cent.
Since early summer of 2020, “long haulers” have described a constellation of symptoms affecting nearly every organ system in the body, and while there are a number of plausible hypotheses to explain them, none have so far been proven. Even the definition of what, exactly, defines long COVID “is still very much in evolution,” Steven Phillips, vice-president of science and strategy at the COVID Collaboration, said in an interview with the New England Journal of Medicine . While the symptoms are very real, “and really seriously afflict people,” the problem is frustratingly complex, difficult to diagnose and unpredictable, Phillips said. No one knows who is truly at risk or how long symptoms might persist, though scientists like McMaster’s Mukherjee are trying their best to solve the post COVID “conundrum.”
Some have called for greater nuance and a more cautious approach to thinking about long COVID, worried that, without clear, diagnostic tests, some symptoms are being misattributed to SARS-CoV-2. One psychiatry intern at Mukherjee’s own university once characterized long COVID as “largely an invention of vocal patient activist groups,” helped along by uncritical media coverage. Some studies have found that people who report symptoms don’t always have evidence of antibodies against SARS-CoV-2. “The long COVID thing,” Sir John Bell, a Canadian immunologist and regius professor of medicine at the University of Oxford, told Times Radio, “has been slightly overblown, and as soon as you do proper epidemiological studies you find the incidence is much, much lower.”
But Mukherjee and other researchers calculate that even by the most conservative estimate — according to the World Health Organization, one in 10 people infected with COVID will experience symptoms lasting beyond 12 weeks — for Canada, that would be on the order of 200,000 people. “Staggering numbers,” said Dr. Fahad Razak, an internist and epidemiologist at St. Michael’s Hospital in Toronto. “Anyone can be impacted by this, young and old alike, and even if you were asymptomatic during initial infection.”
The pathophysiology, the underlying biological causes, are not at all clear. Is it an immune response gone chaotic? Fragments of virus lurking inside the body? Super infections? Micro-clots in the blood?
Various terms have been used to describe it, further complicating things, from chronic COVID and long COVID to the most recent “post-acute sequelae of SARS-CoV-2” or PASC. And while post-COVID symptoms are being seen in children, “the data is even skinnier when it comes to the under 18,” Mukherjee said.
According to the Public Health Agency of Canada, post-COVID conditions are defined as one or more symptoms persisting or recurring 12 weeks or longer after a COVID diagnosis that are not attributable to any other diseases. Symptoms are wide ranging, from the most frequently reported — fatigue, headache and brain fog — to the more rarely reported, such as paranoia.
We have to be really cautious about not under-appreciating how chronic and persisting these symptoms can be
Those who experience severe, or life-threatening infections may be at slightly higher risk. Anyone who spends time in an intensive care unit, whether for COVID or sepsis, can acquire life-transforming complications, according to research by the University of Toronto’s Margaret Herridge, co-leader of a study looking at one-year outcomes in people infected with COVID.
Herridge’s research into post-intensive care syndrome has found that people who spend a week or longer in an ICU, immobilized and heavily sedated on a ventilator can experience fatigue, nerve and muscle injury that can last months after they’re sent home, as well as cognitive dysfunction that messes with memory, attention and problem solving. Anxiety, depression and PTSD occurs in 25 to 35 per cent of ICU survivors.
“With millions of individuals contracting COVID-19 worldwide, an unprecedented number of intensive care unit (ICU) survivors are now in recovery,” Herridge and colleagues wrote in The Lancet.
But people can develop long COVID even after what was initially a mild, or even symptomless infection.
Other viruses, including other coronaviruses, can affect some people for years. “This has been seen post influenza, it’s been seen after SARS,” Razak, of St. Mike’s, said. Studies on survivors of the SARS outbreak in 2004 showed lung abnormalities, one year out. Others were left with severe, disabling fatigue that lasted four years. “We have to be really cautious about not under-appreciating how chronic and persisting these symptoms can be,” Razak said. The fatigue and cognitive effects can affect basic activities of daily life, he said. Getting out of bed. Bathing. Caring for children.
Yet there is “absolutely” still skepticism among the medical and scientific community “because we’re dealing with a condition that is new,” said Razak, first author of an Ontario Science Advisory Table brief on long COVID. People have described doctors waving off their symptoms as being unrelated to COVID, and employers questioning sick time. Razak was skeptical himself going into writing the science table brief. After reading the available literature he became convinced that “we are dealing with a real entity here.”
Risk factors might include having a higher body mass index, being female, being older and having a “higher acuity” of SARS-CoV-2 infection, according to the science table brief. Vaccination reduces the probability of developing it, by greatly reducing the chance of becoming infected in the first place.
There's a whole neuroscientific literature now to show that when the immune system is activated it does have a very localized effect on your brain
Emerging evidence also hints that vaccination reduces the risk of long COVID in breakthrough infections. Some people report symptoms improved after their second dose, which might buoy the notion that the problem could be due to reservoirs or fragments of virus, Imperial College London researchers wrote in The Lancet .
As for the long-term prognosis, a study published in The Lancet, the longest follow-up study to date involving COVID hospital survivors infected in Wuhan’s first wave found that, at 12-months follow-up, most had returned to their original work and original lives, and that those with “persisting, severely impaired health status are rare.” However, 24 per cent of people who were employed before COVID didn’t return to their pre-COVID level of work, and 12 per cent hadn’t returned to work at all. “Our data suggest that a full recovery after 1 year is not possible for some patients, for whom it will take longer to attain their baseline health state before COVID-19,” the researchers reported.
The Chinese team found evidence of persistent abnormalities in lung structure and function. Razak believes much of the pathophysiology likely isn’t related to the original infection and damage to the organs. “It has to do with things that happen after,” he said, like an immune-related phenomenon — an excess and runaway immune response to the virus — or increased clotting.
Some researchers have provocatively suggested other elements might be at play.
A controversial French study involving nearly 27,000 people whose blood was screened for antibodies to SARS-CoV-2 found that people who believed they had been infected, but whose infection couldn’t be confirmed by the antibody test, were more likely to report symptoms of long COVID.
“Beliefs regarding the causes of these symptoms may influence their perception and promote maladaptive health behaviors,” the French scientists wrote, the implication being that some people who have symptoms attributed to long COVID perhaps never had COVID.
But serology tests that screen for antibodies can miss previous infections, and antibody levels wane over time — it’s the very reason health leaders are pushing vaccine booster doses. The authors’ conclusion “reiterates a damaging narrative, implying that long COVID is a psychological disease and that by taking steps to avoid symptom exacerbation, patients are effectively making themselves sick,” Dr. Jeremy Rossman, honorary senior lecturer in virology at the University of Kent said in an expert reaction.
Multiple studies show people infected with SARS-CoV-2 can have physiological symptoms that just aren’t present in the uninfected, Rossman said.
Under WHO’s definition of long COVID, there’s no need for proof of a lab-confirmed infection. It includes a history of probable infection, acknowledging that many people didn’t have access to testing early in the pandemic.
Still, colleagues have asked Razak, of St. Mike’s, how is it possible that one condition could cause such a dizzying array of symptoms? More than 100 have been ascribed to it, though the “one most reported, and most debilitating, is terrible cognitive problems, terrible brain fog,” said Toronto psychiatrist Dr. Roger McIntyre. “People say they have absolutely no energy and absolutely no motivation.”
“There’s a whole neuroscientific literature now to show that when the immune system is activated it does have a very localized effect on your brain,” said McIntyre, who is now testing the antidepressant vortioxentine for post-COVID syndrome . In people with depression, the drug has been shown to improve cognitive function — it makes thinking sharper and clearer — and boost energy and motivation. McIntrye said he’s not implying that post-COVID means people necessarily have depression. “There’s no implication this is depression. There is no indication that this is mental illness. We just happen to be repurposing this medication for this very, very difficult to understand condition.”
It’s not known whether the hyper mutated and fast-spreading Omicron variant, which preliminary data out of South Africa suggests causes milder disease than Delta, will make things any different. Would it mean less long COVID if people are less sick to begin with, or several-fold more cases, as more people ultimately become infected?
For her study, Mukherjee has recruited people who are up to 15 months post COVID diagnosis. On lung function tests, physiologically they look fine. But even a simple, six-minute walk test, “and the shortness of breath comes back, the chest pain comes back, the heart rate increases crazily.”
“We need to find out what exactly is happening,” Mukherjee said. “We need to do studies in bigger numbers, in collaborations, over time. And the people who are fighting this, who are going through this, need to come and get themselves enrolled in studies, and stick to the study, so that we can understand this disease.
“Because unless we understand it and see it and report it and be honest about what we are seeing, we’ll not be able to get to the bottom of this.”
• Email: [email protected] | Twitter: sharon_kirkey
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COVID-19 and loss of smell: what we know
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One of the most curious symptoms of COVID-19 is loss of smell. It can occur during the illness and linger for weeks, months or years. It can also crop up after the infection goes away. This makes loss of smell a common symptom of long COVID-19.
Long COVID can affect vaccinated or unvaccinated individuals, regardless of the severity of infection. Our understanding of long-COVID is still evolving, and scientists and doctors are studying the individual symptoms and how to support people affected by them.
Loss of smell, even temporarily, was one of the primary indicators of a COVID-19 infection early in the pandemic.
“Millions of people around the globe have suffered this symptom during the pandemic,” said Dr. Timothy Smith, ear, nose and throat specialist at Oregon Health & Science University. “We found that probably 80% of those patients who have a loss or distortion of their sense of smell will recover that sense about one to three months after the COVID-19 infection has resolved. But that still leaves up to 20% of people who have an ongoing disturbance in their sense of smell.”
Dr. Smith has spent decades treating patients who lost their sense of smell due to viral illnesses. He says the symptom falls into one of three categories: 1 – total loss (anosmia), 2 – partial loss (hyposmia) or 3 – distorted sense of smell (parosmia).
How smelling works
The smelling process begins at the base of the skull, where the skull bones meet the nasal cavity. The skull bone contains nerve fibers called olfactory nerves, which sit at the top of the nasal cavity and receive air, along with any scented molecules the air carries. These molecules get funneled up the nose into the narrowest portion of the nasal cavity. From there, the olfactory nerves are stimulated, sending information to different regions of the brain for processing, such as those that deal with emotions or memory.
“Many people have had the experience of smelling something over the holiday season that reminds us of our childhoods. But we’re really in our infancy of understanding all the communications that occur within this neural network in our brain,” Smith said.
Our sense of taste is closely tied to our sense of smell. While they have different nerves, a portion of our “taste buds” activate when a food’s flavor bypasses the palate and goes into the nasal cavity, where it gets processed by the olfactory nerves.
COVID-19’s impact on olfactory nerves
“The SARS-CoV-2 virus might not affect the olfactory nerves directly ,” Smith said. “There’s some good evidence showing the virus might injure the supporting cells around the nerves. If the supporting cells that provide nutrition to the nerves are injured, the olfactory nerves themselves may be secondarily injured.”
Nasal or sinus congestion (swelling) during the early stages of a COVID-19 illness also prevents smell molecules from getting where they need to be—the narrowest point in the nasal cavity— to be sensed. By the time the swelling caused by congestion goes down, the damage to the olfactory nerves may be done.
The mental impact of loss of smell varies, but in some cases can be extreme. Lack of sensory input from smell can dull the world around you. And some people may not lose their sense of smell, but rather their sense of smell gets distorted. When that happens, otherwise normal odors can smell terrible to them, making it difficult to enjoy food or everyday experiences.
“The most common distortion I hear in my clinic is one of smoke,” Smith said. “Imagine smelling a grapefruit, but it smells like smoke. Sometimes, nice-smelling things can smell like rotting trash, and that can be really disruptive to someone’s quality of life.”
Another concern for those who have lost their sense of smell is safety. Our sense of smell helps keep us safe, in ways we may take for granted. For example, Dr. Smith advises patients to make sure they have working smoke and gas detectors. Rotten food smells bad, warning us not to eat it, so people who have a compromised sense of smell should take extra care to check expiration dates on their food.
Medical treatments for smell loss or distortion are still in development, but anyone can practice smell training therapy at home.
“Smell training therapy is not invasive, relatively inexpensive and has probably the best evidence behind it,” Smith said. “It consists of spending a few minutes each day, a couple of times a day, smelling two or three or even more essential oils. It’s like physical therapy that you might have after a knee operation or a hip replacement: going back to the basics and retraining those muscles to develop the coordination and strength around the impacted area. The same thing appears to be true with these olfactory nerves as they become injured.”
No particular essential oil is more effective in therapy than others. What’s important is stimulating the olfactory nerves, so choose oils with scents you enjoy.
Working to retrain your nerves takes time but is the easiest way to see results. Most guidance recommends starting with three or four essential oils, smelling one for 10 seconds, pausing for 10 seconds, and moving the next. Repeat this process twice a day.
Dr. Smith would take it a step further.
“I’d smell cinnamon and think or say to myself, ‘This is what cinnamon smells like,’ just to try to get all of those connections working again.”
The longer someone experiences smell loss or distortion, the more challenging it can be to reverse. Dr. Smith recommends patients seek care and start at-home smell training therapy soon after their sense of smell has been affected.
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Losing Your Sense of Smell Is No Longer a Reliable Sign of COVID
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- A recent study found that the risk of smell and or/taste loss from COVID-19 has dropped significantly compared to the early days of the pandemic.
- If you’ve lost your sense of smell and taste, it does not necessarily mean that you have COVID. However, just because you haven’t lost your sense of smell does not mean that you definitely are not infected.
- It’s not clear why the risk of losing your smell from COVID has gone down, but it’s possible that immunity from vaccinations or previous infection and mutations in the virus are playing a role.
The presence or absence of smell and taste loss is no longer a reliable way to tell if you’ve got COVID or not.
After looking at the National COVID Cohort Collaborative database—one of the largest collections of clinical data in the country for COVID research—researchers found that the loss of smell as a key indicator of COVID infection has dropped drastically over time.
Evan Reiter, MD , lead author of the study, professor of otolaryngology in Virginia Commonwealth University’s School of Medicine, and medical director of VCU Health’s Smell and Taste Disorders Center, told Verywell that early in the pandemic, “a viral syndrome with smell loss was very likely to be COVID, but this is not true today.”
Here’s what you need to know.
COVID Symptoms Have Changed Over Time
For the recent study , the researchers focused on data from specific periods when there were peaks in COVID cases. From there, they identified patients who had and did not have smell and taste loss within two weeks of getting a COVID diagnosis.
In 2020, smell and taste loss for the Alpha and Delta COVID variants was more common and even touted as being a classic sign you were infected. With the emergence of newer variants like Omicron and XBB, the researchers wanted to see if the risk of losing those senses is different now.
Instead of looking at the absolute risk of loss of smell and taste, the researchers wanted to see how much the risk changed when they compared the earlier days of the pandemic to more recent times. What they noticed was that from 2022 to early 2023, the risk of smell loss with COVID was only about 6% of what it was back in 2020.
Why Did the Risk of Smell and Taste Loss with COVID Drop?
The researchers say it’s not clear why the risk of smell and taste loss with COVID has decreased so much, but they’ve got some theories.
Reiter said it could be the protective effect of immunity from vaccines or a previous COVID infection—for example, maybe the body’s sense of smell has more protection against damage from the virus. It’s also possible that differences in the virus’s spike proteins as it has mutated have affected its ability to target smell-receptor (olfactory) neurons.
Jill Foster, MD , director of the Division of Pediatric Infectious Diseases at the University of Minnesota, told Verywell that even though the mechanism isn’t totally understood, our ability to smell is complex, and there are many ways the sense can go wrong.
Foster explained that scent first has to come into contact with a receptor in your nose. Then, the message received from the scent gets transmitted to different parts of the brain for processing. Having a cold can plug those receptors, and that’s why you may temporarily lose your sense of smell and taste when you’re sick.
However, Foster said that “COVID goes one step further and can damage the receptors, the nerves that carry the message, and/or the part of the brain that decodes the message.”
Overall, Foster said it’s hard to predict who will lose their sense of smell and taste from COVID, and whether those symptoms will turn out to be long-lasting .
What Are the Common Symptoms of COVID Today?
Recent reports have included that fever is the most common non-respiratory symptom of COVID. Reiter said that symptoms like congestion and a runny nose also seem to be more common.
According to Reiter, the current symptoms of COVID are similar to those seen in prior waves, but the illness seems to be milder and harder to tell from other non-COVID viral upper respiratory infections.
Foster said that while cough, shortness of breath, fatigue, body aches, and, less commonly, sore throat and diarrhea, are other symptoms to watch out for, “it’s important to remember that someone can have COVID-19 and have no symptoms at all.”
Remember that having a single negative antigen test result cannot rule out COVID. According to the Centers for Disease Control and Prevention (CDC), you should test again (at least once) in 48 hours if you’ve had a negative at-home COVID test but you have symptoms. If you don’t have symptoms and have tested negative twice, the CDC recommends taking a third test 48 hours after the second to be sure. To avoid having to do multiple tests, you might want to ask your provider if it would make more sense to have a PCR test done.
Foster cautioned that even then, testing is not perfect.
“It requires testing at the right time of the disease, getting a good specimen from the nose, and being able to perform the test correctly,” she said. “Make sure you test regularly and administer the test properly to detect if you have COVID-19 and seek appropriate care.”
What This Means For You
Losing your sense of taste and smell are no longer reliable indicators of having COVID. If you have symptoms like congestion, runny nose, and a fever, take an at-home COVID test. If your result is negative, take another one in 48 hours or ask your provider if it makes more sense to get a PCR test instead of doing serial testing at home.
The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page .
Virginia Commonwealth University. Risk of smell loss from COVID-19 is as low as 6% compared with initial variants .
Reiter ER, Coelho DH, French E, et al. COVID-19-associated chemosensory loss continues to decline . Otolaryngol Head Neck Surg . Published online May 26, 2023. doi:10.1002/ohn.384
Cotton S. Subramanian A, Pearce AK, et al. The effect of SARS-CoV-2 variants on non-respiratory features and mortality among vaccinated and non-fully vaccinated patients . Am J Respir Crit Care Med . 2023;207:A5438. doi:10.1164/ajrccm-conference.2023.207.1_MeetingAbstracts.A5438
Centers for Disease Control and Prevention. Self-testing at home or anywhere .
By Carla Delgado Carla M. Delgado is a health and culture writer based in the Philippines.
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- 17 October 2023
- Clarification 17 October 2023
New pill helps COVID smell and taste loss fade quickly
- Mariana Lenharo
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A new drug can alleviate loss of smell and taste caused by COVID-19. Credit: Angela Weiss/AFP via Getty
New clinical-trial data suggest that an antiviral pill called ensitrelvir shortens the duration of two unpleasant symptoms of COVID-19: loss of smell and taste. The medication is among the first to alleviate these effects and, unlike other COVID-19 treatments , is not reserved only for people at high risk of severe illness.
Early in the pandemic, roughly 40–50% of people with COVID-19 experienced impaired smell or taste 1 . The antiviral drug molnupiravir speeds recovery of these senses 2 , but generally only the most vulnerable people can take it.
That is not true for ensitrelvir. In Japan, where it received emergency approval last year , the drug is available to individuals with mild to moderate symptoms, regardless of their risk factors. Its developer, Shionogi in Osaka, Japan, is continuing to conduct clinical trials of the drug, which has not yet been approved outside Japan.
COVID drug drives viral mutations — and now some want to halt its use
In one such trial, people with mild or moderate COVID-19 symptoms were given either 125 or 250 milligrams of ensitrelvir or a placebo. At the start of the study, 20% of participants reported some level of smell or taste loss. After the third day of treatment, the proportion of participants reporting such symptoms in the ensitrelvir groups started dropping more sharply than did the proportion in the placebo group. At day seven, the percentage of participants with smell or taste loss was 39% lower in the group taking 250-milligram pills than in the placebo group. Three weeks after treatment began, all groups reported similar symptom scores.
The findings were presented on 12 October at IDWeek, a meeting of infectious-disease specialists and epidemiologists in Boston, Massachusetts.
“Most people will eventually recover on their own, but we know that some people have had long-term issues with smell and taste,” says Yohei Doi, an infectious-disease researcher at Fujita Health University in Toyoake, Japan, and one of the study investigators.
A hallmark symptom dwindles
Smell and taste problems are less prevalent now than they were at early stages of the pandemic 3 . “When the Omicron variants became dominant, the loss of taste and smell started to become less and less common,” says Amesh Adalja, an infectious-disease specialist at the Johns Hopkins Center for Health Security in Baltimore, Maryland. “But it still occurs, and it is a distressing symptom.”
Earlier this year, Shionogi reported that ensitrelvir shortens symptoms of COVID-19 by about a day — a standout trait, says Adalja. “What we’re trying to do is not just minimize severe disease, hospitalization and death, but also to minimize the disruption that an infection has on people’s activities.”
Updates & Corrections
Clarification 17 October 2023 : This story has been amended to reflect ensitrelvir’s regulatory status outside Japan.
Yong, J. Y. T., Wong, A., Zhu, D., Fastenberg, J. H. & Tham, T. Otol. Head Neck Surg. 163 , 3-11 (2020).
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Reiter, E. R., Coelho, D. H., French, E. Costanzo, R. M. & N3C Consortium. Otol. Head Neck Surg. https://doi.org/10.1002/ohn.384 (2023).
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The Iatsenko lab is looking to recruit one PhD student for a project at the MPIIB starting 2024 within the IMPRS-IDI graduate program.
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Tenure-Track Assistant Professor, Associate Professor, and Professor
Founded at Hangzhou, China in 2018, Westlake University is a new type of non-profit research-oriented university, creating a stimulating, world-cla...
Westlake Center for Genome Editing, Westlake University
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