• Katie Phillips, MD

How COVID-19 Affects Taste and Smell

Updated: Dec 7, 2020

A clever data scientist looked at the product reviews of scented candles over the last year and found the overall rating of scented candles has decreased in this time span correlating with the introduction of the Coronavirus disease 2019 (COVID-19) pandemic.(1) While we cannot be sure why product reviews for scented candles have gone down, one can speculate that perhaps in the midst of a global pandemic that is known to cause taste and smell disorders, it could be that many scented candle customers have COVID-19 and cannot smell their candles and are therefore leaving poor reviews.



Almost a year into this global pandemic, we now know that Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which causes COVID-19 is associated with both smell and taste loss. This is not a unique phenomenon to this virus, and in fact, many other respiratory viruses have been linked to smell loss; although smell loss seems to be particularly widespread in COVID-19 patients. There have been a wide range of reported taste and smell dysfunction associated with COVID-19. In a recent study of patients with mild to moderate COVID-19, 85.6% of patients reported smell loss and 88% of patients reported taste loss.(2) Today, the Johns Hopkins Coronavirus Resource Center website reports nearly 65,500,000 cases of COVID-19 globally which extrapolates to millions and millions of people with taste and smell dysfunction. The other thing to recognize is that taste and smell are closely related. Much of your sense of flavor is actually from the odors of the food. Therefore when you lose your sense of smell, your sense of taste or flavor of food is drastically altered.

The good news is that most patients completely recover both their sense of taste and smell within a relatively short period of time. The chart below is taken from an article which studied patients from Europe and displays the percentage of patients who recover their smell function within a specified amount of days.(Figure 1)(2) The majority of patients in this study recovered their smell function within 8 days and only 3.3% of patients were left with some amount of smell loss after 15 days.


Figure 1 reproduced from Lechein JR et al.


Although it is a small percentage of patients that are left with lingering smell or taste loss, this still accounts for a large number of patients given the sheer amount of people who have been infected with SARS-CoV-2. Although this inability to completely taste and smell may seem like a small problem to those who have never experienced this issue, it turns out to have several ramifications.

Multiple studies have shown that smell and taste loss can decrease your quality of life, your ability to enjoy food, your social interaction with others, and increase your risk of depression. Additionally, if you cannot smell you are also at risk for certain dangerous situations such as not being able to notice a fire or natural gas leak because you cannot smell the smoke or gas. You may also be more likely to eat expired or rotten food because you cannot smell or taste. Finally, studies have also found an association between smell loss and the odds of dying within the next 5 years.(3-5) (Although these studies have only shown an association without an explanation of the underlying cause, so it may be that there is a hidden factor at play in this association.) All this to say, if you have long standing problems with smell and taste, there may be lasting consequences.

So what should you do if you have lasting smell and taste loss after having COVID-19?

The first thing to do is to mention this to your doctor. They may want to rule out any other causes of smell and taste loss first. Chronic sinus problems (chronic rhinosinusitis), neurological diseases (dementia, Parkinson’s disease), tumors (either in your nose or brain) or head trauma can also cause smell and taste disorders. Your doctor will be helpful in checking for these problems.

It may then be worthwhile to understand what level of smell loss you have. Smell loss can be measured through various tests such as the University of Pennsylvania Smell Identification Test (UPSIT) or the Sniffin’ Sticks Test. These tests give you a measure of your smell loss and can categorize your smell loss as complete smell loss (known as anosmia) or a decrease in sense of smell (known as hyposmia). This is important because the severity of smell can give you some idea of how you will ultimately recover. In other words, those with more severe smell loss may have less of a chance of complete recovery.

One particularly interesting thing that can happen as your brain works to regain your sense of smell is that you may develop something called parosmia. This is a process where your brain distorts a smell, causing something to smell different (and often more unpleasant) than normal. For example, the smell of freshly baked cookies may smell like rotten onions. No one knows for sure why this occurs. People have hypothesized that perhaps some of the smell system is destroyed and when the brain tries to “rewire” there is an incomplete set of smell nerves which creates this distorted odor. Others have hypothesized that the “rewiring” process is slow in some people and the cells are immature creating a distorted odor. This is usually not permanent but can last several months to years when we have studied this phenomenon in other types of smell loss. We will learn more about what parosmia means for COVID-19 patients as time goes on, but for now if this occurs to you - know that this is a known phenomenon associated with smell loss and you are not crazy.



One method of treatment that has been shown to be helpful in other instances of smell loss after respiratory viruses is Olfactory Training.(6) Olfactory training was developed by Thomas Hummel in 2009 and is thought to work by “retraining” your brain by creating new connections in a situation similar to physical therapy after a stroke. The training involves picking four odors from four distinct odor categories (usually lemon, clove, eucalyptus and rose). You then smell each odor and concentrate on the particular odor you are smelling. For example, you would smell rose and tell yourself “I am smelling rose”. This is done for 15 seconds with 10 seconds between each odor and then repeated. This process is completed once in the morning and once at night for 4-6 months.(6) You can buy olfactory training kits or make your own by purchasing essential oils or using the real ingredients. Some people find it useful to journal through this training to monitor this progress. Before starting, it is good to know that recovery is slow and you may not ever make a full recovery. Unfortunately in some instances, you may not make much progress at all. Yet, there are few risks to this therapy, so if there is a chance to recover some smell function it is worthwhile to try.

Key Takeaway Messages

  • Smell and taste dysfunction is common among patients with COVID-19

  • Most people recover their sense of taste and smell within the first 8 days

  • For those left with lingering smell and taste problems, discuss this problem with your doctor

  • Olfactory Training may be helpful for those with lingering taste and smell dysfunction after recovery from COVID-19

References

  1. https://twitter.com/kate_ptrv/status/1332398737604431874

  2. Lechein JR, et al. Olfactory and gustatory dysfunctions as a clinical presentation of mild-to-moderate forms of the coronavirus disease (COVID-19): a multicenter European study. Eur Arch Otorhinolaryngol. 2020;277(8):2251-2261

  3. Pinto JM, Wroblewski KE, Kern DW, Schumm LP, McClintock MK. Olfactory dysfunction predicts 5-year mortality in older adults. PLoS One. 2014;9(10):e107541.

  4. Liu B, Luo Z, Pinto JM, et al. Relationship Between Poor Olfaction and Mortality Among Community-Dwelling Older Adults: A Cohort Study. Ann Intern Med. 2019;170(10):673-681.

  5. Van Regemorter V, Hummel T, Rosenzweig F, Mouraux A, Rombaux P, Huart C. Mechanisms Linking Olfactory Impairment and Risk of Mortality. Front Neurosci. 2020;14:140.

  6. Damm M, et al. Olfactory training is helpful in postinfectious olfactory loss: a randomized, controlled, multicenter study. Laryngoscope. 2014;124(4):826-31.


As always, the content in this blog is meant to be informational and not serve as a substitute for a medical evaluation with a physician.


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