How Covid-19 Affects Taste and Smell

One of the most mysterious symptoms of Covid-19 is the loss of taste and smell. Not all people who come down with the illness experience this phenomenon. But those who do can lose their ability to taste and smell for months at a time. Some regain these senses only to find that their perception of good and bad tastes and smells has been reversed. 

Scientists at the Monell Chemical Senses Center in Philadelphia, Pennsylvania estimate that 37 percent of people had some form of taste loss after a coronavirus infection. To learn more, Science World spoke to Hong Wang, a molecular biologist at the Monell Center. She discussed what scientists know—and are still trying to uncover—about how Covid-19 negatively affects our senses.

We are still trying to figure this out. To study this phenomenon, we test people using scratch-and-sniff cards with different scents to determine who may or may not be experiencing a lost sense of smell. We can also collect a sample of their epithelium tissue to analyze for any molecular changes. 

Spotting these changes could help scientists understand how exactly Covid-19 causes a loss of smell. For instance, inflammation, caused by the body’s reaction to the illness, may cause the olfactory system to function improperly. That can affect the way people process smell information in the brain. If our sense of smell changes, so does our ability to detect different flavors.

We still need to figure out why some people’s loss of smell lasts so long after they’ve recovered from the Covid. Some genetic, or inherited, factors may put people at higher risk of long-term loss of smell, but these factors may not be the only cause. 

We also don’t know why good and bad smells and flavors get mixed up for some people. The neurons—cells that make up nerves—that carry scent information to the brain are well organized. We think the illness may change that organization. So when your nose smells one thing, your brain processes it as something else. But that’s just a hypothesis, or a proposed explanation for a phenomenon.

If you notice that you’ve lost your sense of taste or smell, you should see your doctor and seek medical advice. Right now, there isn’t an effective medicine to treat smell and taste loss. Olfactory training seems to be helpful for some patients. That’s a type of therapy where the patient sniffs a new scent every day to retrain their nose. Sometimes, exposure to a smell signal over and over again can remind the brain how to detect that scent more easily in the future. Eventually, the brain can relearn other smells and make progress toward getting the general sense of smell back.