Early on in the pandemic, a diminished sense of smell (known as anosmia) and taste (known as ageusia) was reported anecdotally around the world in conjunction with the coronavirus. In late March, ENT UK—the professional society of ear, nose, and throat specialists in the United Kingdom—published an advisory on evidence from South Korea, China, and Italy that "significant numbers" of people who tested positive for COVID-19 also lost their sense of smell and taste. (Loss of taste is often a manifestation of loss of smell.) For some patients, loss of smell was the only symptom they experienced, while for others it occurred along with other symptoms such as fever.
Based on these and subsequent reports, the World Health Organization (WHO) added anosmia and ageusia to the list of symptoms of COVID-19. Even before WHO declared these official symptoms, the American Academy of Otolaryngology-Head and Neck Surgery had recommended that they be added to the list of symptoms when screening for COVID-19 in patients.
Confirming loss of smell as a COVID-19 symptom, especially an early one, is important for several reasons: It should prompt people who experience it to contact their doctor about testing and other symptoms to watch for, or to self-quarantine to avoid possibly transmitting the virus to others.
Studies are underway to determine how COVID-19 causes a loss of smell. Human clinical examinations and studies on mice suggest that virus-induced inflammation and swelling in the nasal cavities may damage the olfactory receptor cells (collectively termed the olfactory nerve) and other cells within the olfactory region. The virus' influence on the olfactory nerve may temporarily or even permanently alter a person's ability to smell. Researchers at Harvard believe the virus may affect cells inside the nose rather than the olfactory nerve. Some people with COVID-19 who have lost their sense of smell and taste have reported a return of function within a few weeks; many others, however, have not noticed such a return.
Loss of smell is a known symptom of some neurologic conditions, such as Alzheimer's disease, multiple sclerosis, Parkinson's disease, and cranial neuropathies (conditions in which nerves of the brain or brainstem are damaged), and can occur after a more common viral infection. It also can result from other medical causes such as nasal congestion and polyps, injury to the nerves that control smell due to surgery or head trauma, exposure to toxic chemicals (such as pesticides and solvents), some medications (including anti-inflammatory drugs and antibiotics), radiation for head and neck cancers, hormonal problems, and age, as well as cocaine use.
While losing your sense of smell might not seem significant compared with other health problems, it can have far-reaching consequences: for example, not being able to smell smoke or a gas leak or taste that food has gone bad. It also can result in nutritional deficits, weight loss (which can be dangerous for people who have trouble retaining weight), and isolation if it becomes depressing to eat with others when you can't taste the food.
For those who do lose their sense of smell due to the coronavirus—or anything else—regularly sniffing a variety of odors may help smell function return. Try strong scents like rosemary, curry powder, lavender, or other pungent herbs. Taking certain antioxidants, such as alpha-lipoic acid, also may help. To compensate for a loss of taste, focus on texture—the crunch of a carrot or the juice of a berry in your mouth, for instance.
For more information about losing this sense, including recipes for people who can't smell, check out Navigating Smell and Taste Disorders by Ronald DeVere, MD, FAAN, and Marjorie Calvert (Neurology Now Books; Demos Health, 2010).
Dr. Doty is the director of the Smell and Taste Center at the University of Pennsylvania’s Perelman School of Medicine in Philadelphia.
