MIT Medical answers your COVID-19 questions. Got a question about COVID-19? Send it to us at CovidQ@mit.edu, and we’ll do our best to provide an answer.
I tested positive for COVID-19 back in September. My loss of smell and taste was quick and drastic. Since then, my sense of smell has slowly and partially returned. But three months later, my sense of taste remains drastically reduced. I can somewhat taste foods that are strong with flavor, but for most foods, there’s still nothing. Will my senses — especially my sense of taste — get back to their pre-COVID levels? Are there any treatments that might help?
These are among the most common questions we get these days. Sadly, you are far from alone in experiencing an ongoing loss of smell and/or taste following recovery from COVID-19. But unfortunately, at this point, there is no proven treatment and no guarantee of full recovery.
Though it took the CDC a few months to recognize “new loss of taste or smell” as a possible symptom of COVID-19, anosmia, loss of smell — often accompanied by ageusia, loss of taste — has become a hallmark of the illness. It’s the symptom most predictive of a positive PCR test and the most prevalent overall (at least in Europe and North America, particularly in individuals with mild cases). A recent meta-analysis estimated the proportion of affected patients at 41 percent overall but noted that higher numbers were found in studies using objective measures of smell and taste rather than relying on self-report. One such study found that 59 of 60 COVID-19 inpatients — a whopping 98 percent — demonstrated at least mild olfactory dysfunction compared to age- and sex-matched controls.
While it’s clear that loss of smell and taste happens with some frequency in COVID-19, the why has been a bit more difficult to suss out. It’s different from colds or flu, where smell and taste may be affected by nasal congestion; a stuffy nose is not a typical symptom of COVID-19, and radiographic imaging of affected individuals usually fails to show significant nasal or sinus inflammation. Early on, some scientists thought that COVID-related anosmia meant that the virus might be infecting olfactory neurons or using those neurons to infect the brain, but studies have shown that this is unlikely. Rather, it now appears that the virus attacks the neurons’ helper cells in the nasal cavity. Among other functions, these cells provide metabolic and physical support to the cilia, fingerlike odor receptors on the neurons’ surfaces. And unlike mature olfactory neurons, their surfaces are peppered with angiotensin-converting enzyme 2 (ACE2) receptors, through which the SARS-Cov-2 virus enters the body’s cells.
We know less about how the virus causes loss of taste. It may be related to olfactory dysfunction, since odors are a crucial part of flavor perception. But true ageusia, where people cannot detect even sweet or salty flavors, can also occur. Some individuals with COVID-19 even lose “chemical sensing” — the ability to detect, for example, the burn of spicy food, which is moderated by pain-sensing nerves. While taste receptor cells do not contain ACE2, other support cells in the tongue do, as do some pain-sensing nerves in the mouth, so these cells may be susceptible to infection.
Many of these cells can regenerate. But things can get strange before they get better. Individuals recovering from COVID-19 often report parosmia — odd and often unpleasant distortions in the senses of smell and taste, even phantom odors. But all of this weirdness is usually a sign of progress. It means that new neurons are being created and working to connect with the brain’s olfactory bulb. Axons may connect to the wrong place, causing parosmia, but these wiring errors can correct themselves over time.
So, how long is it going to take? It’s impossible to say. In a study of 54 French patients with COVID-related anosmia, all but one reported full recovery within 28 days. But other studies have had less optimistic results. In a Danish study, 41 percent of individuals with taste dysfunction and 48 percent with olfactory dysfunction reported they had not fully regained those senses after six weeks. An Iranian study showed that 37 percent of subjects with COVID-related olfactory dysfunction continued to score below normal on scent tests after six to eight weeks. Another found that nearly five percent failed to recover olfactory function by six months.
On the other hand, a long-term study of post-viral olfactory dysfunction published in 2014 showed that some individuals who lost the sense of smell after, for example, influenza, continued to show improvement after as long as two years. But we don’t know if recovery after COVID-19 will follow a similar pattern. And it’s too soon to know whether some COVID-related loss of smell or taste will be permanent.
At this point, there is no proven treatment for COVID-related olfactory dysfunction, but research on other types of post‐viral olfactory dysfunction may be relevant. A comprehensive, evidence‐based review of treatment options published last summer evaluated the use of systemic and topical steroids, non-steroidal topical and oral medications, olfactory training, and acupuncture. Based on a risk-benefit analysis, the authors recommend olfactory training and note that healthcare providers may choose to try topical and/or systemic steroid treatment in individual cases. You might also want to check out some of the recipes in Taste & Flavour. Available for free download, the cookbook was created by a British chef in collaboration with scientific experts, and contains recipes intended to stimulate the taste buds of individuals recovering from COVID-related loss of smell and taste.
“How and when will I be able to smell and taste again?” When we decided to tackle this question, we assumed the answer would be pretty straightforward. However, as with many other COVID-related questions, it was anything but. Though they can be carried to us through such humble vehicles as burritos and body lotion, tastes and smells are part of complex physical systems. And while the Internet might think it’s funny to eat an entire onion without tasting it, the loss of taste and smell is a powerful loss, indeed. Even if this loss turns out to be temporary, you are allowed to mourn it. Connecting with others can help, and social media sites like Facebook have groups where you can talk about your experiences and share resources. AbScent, a UK organization supporting those affected by anosmia, has resources and guidance on smell training, and also runs a large Facebook forum on the topic. It may also help to take time to appreciate your other senses: spend time outdoors, listen to music, or luxuriate in comfortable clothing. Above all, be kind to yourself, and remember — you’re not alone.
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