The Mystery of Why People With Covid-19 Lose Their Smell and Taste

As the coronavirus crisis escalated across the globe in March, some people with Covid-19 began reporting strange symptoms: the sudden inability to smell or taste.

Near the end of the month, doctors around the world began acknowledging that some Covid-19 patients had these symptoms. By that point, however, most of the reports about the symptoms were anecdotal, shared by doctors on medical message boards. Public health institutions seemed to hesitate to make formal statements on the symptoms’ significance while more and more people shared stories about the inability to smell a diaper or taste the tang of vinegar. It took until April 27 for the Centers for Disease Control and Prevention to say that “new loss of taste or smell” was a potential sign of Covid-19.

Now, formal studies on the unusual symptoms are trickling in. Today in the journal JAMA Otolaryngology-Head and Neck Surgery, Italian doctors detail their research on the frequency of these symptoms in 204 Covid-19 patients interviewed over the phone.

As the early anecdotes predicted, the symptoms were fairly common in the sample: About 57% reported a reduction in taste, smell, or both. Nearly 40% had a severe reduction in taste, and about 35% had a severe loss of smell. While a few studies on these symptoms have already been published, the authors note that theirs is the only one that used the validated otolaryngology questionnaire known as the Sino-Nasal Outcome Test 22 — better known as the SNOT-22.

The SNOT-22 helped answer an outstanding question about these symptoms: Is the loss of smell and taste really caused by Covid-19, or is there just something else stuck in the patients’ noses? In the study, only 14.8% of patients who had a severe loss of taste reported a nasal obstruction, and only about 16.7% with a severe loss of smell did the same, suggesting that the symptoms really are related to the coronavirus.

One of the most interesting observations the researchers made is that these symptoms tended to appear before the person was even diagnosed with Covid-19 — a median time of four to seven days before diagnosis. This means that a general practitioner, keeping an eye out for these symptoms, could play a “pivotal role” in identifying people who might have Covid-19 at an early stage of the disease and asking them to self-isolate.

There’s still a lot left to learn about these symptoms, including why they’re the only symptoms that manifest in some people, and whether they really are the mark of an otherwise asymptomatic carrier. But at the very least, the new research increases confidence in the idea that these symptoms are an early sign of Covid-19. As public health experts underscore the importance of early diagnosis and quarantine, we could use all the forewarning we could get.