Why Does COVID-19 Destroy Our Sense of Smell?

COVID-19 symptoms are all over the map, with manifestations that can range from disruptive to downright deadly. The lost sense of smell some sufferers are experiencing is particularly bizarre but it's proven to be so common—with up to two-thirds of COVID-19 sufferers losing their sense of smell to some degree—that physicians frequently use it as a screening symptom for possible testing. Until recently, researchers assumed this was evidence of neurological infection. Now, studies are showing this is unlikely to be the case.

Loss of Sense of Smell Not Uncommon as Coronavirus Symptom

Viruses account for about 40% of all cases involving a lost sense of smell. Up to 15% of those are the result of coronavirus infections, a handful of which (along with about 200 other viruses) cause the common cold. However, the problem may be particularly common in people infected with the much more dangerous SARS-CoV-2, the coronavirus responsible for COVID-19. In fact, as many as two in every three cases of COVID-19 patients could experience some level of loss of smell—that's a lot.

The problem is so prevalent in COVID-19 patients that some researchers have suggested using the symptom as a specific biomarker for the disease. 

COVID-19 Symptoms: What Causes the Lost Sense of Smell?

A group of researchers from numerous universities across the world dug deep to put the mystery to rest. In their paper, which they recently published in Science Advances, they share that the symptom isn’t the result of attacks on scent-detecting neurons, which had seemed the most likely reason. In fact, until recently, reporting outlets had run with the assumption that the lost sense was evidence of neurological infection.

But the recent study revealed that there aren’t any ACE2 receptors (SARS-CoV-2’s doorway into our cells) in the neurons that affect the sense of smell, and that means the loss isn’t the result of direct neurological infection—so they were forced to rule that out. This is actually great news for people who’ve suffered this symptom. The lack of direct neurological involvement means the loss is likely only temporary, so most COVID-19 survivors can expect to regain their sense of smell eventually.

The researchers found four other possibilities for the loss of smell phenomenon, though:

• Inflammation from the COVID-19 infection could be blocking off the nerves.
• Damage to cells that support the neurons could cause temporary loss of smell.
• Damage to olfactory glands could have the same effect.
• Vascular damage resulting from inflammation may also impair nose function.

All of these problems are happening to various degrees throughout infection with this virus. So any one of them could be the probable cause and only more research will tell us definitively. Maybe that answer will be the one that leads us to a cure for this awful virus. COVID-19 symptoms have thrown some ugly surprises our way since the first emergence last year, but at least this one is likely to fade with recovery. If you or someone you know suddenly loses their sense of smell, or finds food no longer tastes quite right (a result of the loss of smell), call a doctor right away about getting tested for COVID-19 even if you or they have no other symptoms. And if you’re recovering and still waiting for your sense of smell to return, just be patient, it should come back soon enough. At least, however small the victory, there is some good news there.

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