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Why do so many people with COVID-19 lose their senses of smell and taste?



And what does this tell us about disease severity and more? Here’s what new research reveals.

Up until a year ago, “What’s that smell?” had been a fairly innocuous question. Now we know it can help identify if you’ve been infected with COVID-19.

Losing the sense of smell and taste is one of the most common symptoms of COVID-19. It’s estimated that about 74 percent of people who have COVID-19 lose some or all of their ability to smell – topping the number who experience fever or shortness of breath.

Some researchers have even recommended the use of anosmia, the medical name for loss of smell, as a test to diagnose COVID-19. That’s why it’s recommended to get a COVID-19 test if you’re experiencing a new and sudden loss of smell or taste.

There’s much we’ve discovered about this curious symptom, while there remains a lot unsolved. Here are the latest answers to some common questions:

Why do people with COVID-19 lose their sense of smell?

It was first thought the virus infected specialized neurons in the nose that detect odors and send signals to the brain. Scientists worried that the virus could reach the brain this way.

Recent research has disproven those claims. Now, scientists think that the cells that surround and support these neurons become infected. Without support from these cells, the neurons lose the ability to detect odors. This is actually good news, as once the infection has cleared, these support cells can recover, meaning the loss of smell does not appear to be permanent.

Could it just be a stuffy nose? With other viruses, like the common cold, that’s why smell can disappear temporarily. But COVID-19 does not always cause nasal congestion.

What can loss of smell tell us about the severity of infection?

In one study, almost 55 percent of people who lost their sense of smell had a mild form of the disease. People who survived severe cases reported a loss of smell only about 7 percent of the time.

It’s not yet known why this is so. It could just be that there are so many more mild cases out there. It could also be due to a person’s immune system. People with mild cases of COVID-19 may have better immune responses within the cells of their noses, limiting the virus’s spread to other parts of the body. Further research can help clarify the reasons.

Why is taste also affected?

The senses of smell and taste, combined with a special ability called chemesthesis to detect sensations such as spiciness, allow you to identify the flavor of a food or beverage.

That’s why if you can’t smell aromas, for example, you won’t be able to taste the full richness of a cup of coffee or a strawberry’s sweetness. What’s more, people infected with COVID-19 can also separately lose their sense of taste and chemesthesis.

While we have a few clues about the loss of smell, researchers aren’t certain how the virus causes these other losses. But we do know that when taste returns, it may not be what some people are expecting. Some people have complained that they cannot taste the nuances of salty, sweet and sour, or that everything tastes bland like cardboard or has an artificial flavor.

How long do these losses last?

Nearly all people who’ve lost their senses of smell and taste regain them, either gradually or all at once. But recovery times can vary widely.

The majority of people recover their sense of smell within three weeks. But 15 percent of people may take two months to recover, while about 5 percent of people haven’t regained these senses even after six months.

There aren’t any established treatments proven to speed up the recovery process. Some doctors recommend courses of steroids or plasma infusions. Others may suggest smell training, in which people relearn certain odors by regularly sniffing them.

What effects do these losses have on overall health?

Most people don’t realize the importance of smell and taste – until they lose them. And the consequences can be devastating.

On one hand, if you can't smell and taste things, you can’t detect dangers like rotten food or a gas leak. On the other hand, you may also lose touch with the familiar comforts of life, such as the smell of the outdoors or a roast in the oven. This can be disorienting and scary. People may even lose interest in eating, leading to unhealthy weight loss. These factors can contribute to poor mental health, including depression. As Hellen Keller once said,Smells are the fallen angels of the senses.”

If you’re experiencing a loss of smell or taste, tell your health care provider. They can help you take care of your senses, body and mind.