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COVID-19 is not the only virus that affects our ability to smell, but it's unique in the way in which it does so. For example, the common cold causes an inflammatory response in the nose, and that builds up mucus, which reduces your ability to smell. With COVID-19, however, it is not nasal congestion that causes the smell loss. Rather, the virus gets into the nervous system, affecting the neural connections that are necessary to detect and interpret odor.

COVID-19 affects the nervous system and sometimes results in profound loss or a complete inability to smell. Some people recover their ability to smell within a few days or weeks, but for some people it's been going on for much longer.

"This is really taking its toll on the people who have not had their sense of smell, sometimes for months or more," said Julie Walsh-Messinger, assistant professor of psychology. "It can have real consequences. For example, if you can’t smell smoke, you are relying on a smoke detector to tell you there's a fire. It is also affecting quality of life. Food doesn't taste good anymore because how you perceive taste is really a combination of smell, taste and even the sense of touch. Some people are reporting weight loss due to loss of appetite, and they're just not able to take pleasure in the things that they've previously found pleasurable."

Research also shows that smell impacts decisions we make daily — but may not be consciously aware of. For example, smell can influence our attraction to others. It's one of the ways in which we select mates who are less genetically similar to us, which can be an advantage for reproduction. It can also help us detect fear in others, which is important for survival.

Resources are available to people who have lost taste and smell. For example, smell training retrains the body's ability to detect and identify an odor by smelling it over and over again.

"We are optimistic that the sense of smell will come back for some of the people who lose their sense of smell for several months," said Walsh-Messinger.

This article is adapted from a piece that originally appeared in The Conversation. Walsh-Messinger has also conducted research on how neurodegenerative diseases like schizophrenia impact sense of smell, lingering COVID symptoms among young adults and rehabilitation treatments for COVID-19 "long-haulers."