Ask the doctors 9/22 - Tue, 22 Sep 2020 PST

Dear Doctor: Why are people making a big deal out of the fact that you can lose your sense of smell and taste when you get sick with COVID-19? The same thing happens to me when I’ve got a plain old cold.

Dear Reader: Many of us who have slogged through the unpleasant symptoms of a cold or the flu know that losing your sense of smell and/or often a large portion of your sense of taste, is a common part of the experience. The same has proven to be true with COVID-19. It turns out, however, that this loss of the sense of smell, known as anosmia, occurs for two very different reasons.

Let’s start with a cold and the flu. Our immune systems fight these infections on multiple fronts, including the one-two punch of mucus production and inflammation. This combination does an excellent job of blocking our sinuses. Since the sense of taste is closely linked to the sense of smell, both take a steep dive during the plugged-up phase of an illness. With specialized nerve endings in the nasal passages unable to send a full range of information to the brain, the subtleties of taste are gone. What we’re left with are the broad strokes of bold flavors. That’s why, when we’re fighting a cold or the flu, the sweetness of hot tea with honey or the saltiness of chicken soup tastes particularly good.

When it comes to COVID-19, researchers have recently uncovered the surprising reason for anosmia as one of the earliest symptoms of infection. Rather than congestion, as with a cold or the flu, the loss of smell in people with COVID-19 occurs due to how the virus affects the nervous system. According to a study published by researchers at Harvard University earlier this summer, SARS-CoV-2, the virus that causes COVID-19, attacks certain cells with the job of supporting the olfactory sensory neurons. These are the specialized nerve cells that detect the chemical compounds that make up a scent, known as odorants, and transmit that information to the brain. The brain then decodes the electrical impulses, which allows us to experience them as scent. By damaging the support cells, the virus prevents the olfactory sensory neurons from responding to the molecules that make up different types of scents. The good news is that for most patients, recovery from COVID-19 includes a return of their sense of smell.

As we’ve mentioned here before, researchers are still in the earliest stages of learning about the novel coronavirus and COVID-19. That makes each new bit of information important. As cases began to mount, it became clear that only about half of contagious people presented with a fever as an early symptom. At the same time, it emerged that a loss of the sense of smell was one of the first symptoms of infection. Since early intervention gives people who become ill with COVID-19 a better chance of recovery, this has been a significant finding. Thus, the widespread news stories and discussions that you have noticed.

Send your questions to askthedoctors@mednet.ucla.edu