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Why Some COVID-19 Patients Lose Their Sense of Smell

Why Some COVID-19 Patients Lose Their Sense of Smell

Loss of smell can be an early sign of infection, whether or not you have other symptoms. Learn why, and what to do.

Updated June 10, 2020; 5:00pm ET

At first, there were anecdotes. A handful of doctors around the globe relayed stories of COVID-19 patients who had lost their sense of smell—and frequently, their sense of taste, too. Among some initial reports, it was the first sign of sickness.

But as the weeks went on, a clear trend emerged. A growing number of people with the disease reported losing some or all of their ability to smell and taste. And by April, the Centers for Disease Control and Prevention (CDC) added “new loss of taste or smell” to its official list of disease symptoms.

Now, months into the pandemic, COVID-19’s connection to losing these olfactory senses has been clearly established. But questions remain: Why are these symptoms so widespread? When should you see a doctor? And could some people lose their sense of smell permanently?

Losing the ability to smell is common
Many people with COVID-19 are “silent spreaders” and begin to spread the virus before they develop symptoms, or never develop symptoms at all. But a large proportion report mild to severe signs of illness within two weeks of becoming infected. These frequently include, but aren’t limited to, fever, chills, cough, breathing troubles—and loss of the ability to smell.

Though we will learn more as larger studies are completed, current research suggests that between 50 and 98 percent of people with COVID-19 experience a partial loss of smell (hyposmia or microsmia) or a total loss (anosmia). Sometimes, it’s the only indication that they have the SARS-CoV-2 virus.

Fortunately, this loss may be associated with a milder course of disease. An April 2020 study of COVID-19 patients published in the International Forum of Allergy & Rhinology showed that most participants reporting smell or taste loss didn’t require hospitalization. Why? Some experts theorize the virus remains around the nose in milder cases; it never makes its way down to the chest to cause serious respiratory problems.

COVID-19 can also affect taste
Some people who lose their sense of smell also lose their ability to taste. Doctors aren’t yet sure how many people are affected, however, and whether it’s actually happening at all.

“We don't yet have really good data beyond just case reports and isolated instances of the loss of taste,” says Nicholas Rowan, MD, assistant professor of otolaryngology, head and neck surgery at the Johns Hopkins University School of Medicine in Baltimore. “It is typically less than the loss of sense of smell, though, for sure.”

There’s little data partly because loss of taste is harder to measure. But it’s also due to the nature of taste itself. Your ability to detect flavor is strongly tied to your ability to pick up a scent.

“If you have a stuffy nose, fevers, chills, and you generally feel poor, you lose your sense of smell,” Dr. Rowan explains. “You can't taste that chicken noodle soup that Mom is making you because you're ill and your nose is blocked up.”

So, when people describe losing their sense of taste, he adds, “what patients are describing might actually be a change in the perception of flavor.”

Why COVID-19 may affect smell and taste
There are already some theories as to why COVID-19 influences smell and taste. First and foremost, losing the sense of smell is simply common to many viral infections. Viruses cause inflammation around nasal tissue and within the olfactory nerve, says Rowan, “and that is something that we have been dealing with for decades and decades and decades.”

Many experts believe that SARS-CoV-2 may also work in a different way, too. Cells that support the olfactory nerve and help it function have receptors that make them vulnerable to the virus. So, when SARS-CoV-2 attacks those cells, it could also harm the olfactory nerve cells.

Another theory: Some speculate the virus could infect the olfactory nerve itself.

“We know from the prior studies into similar novel coronaviruses—SARS-CoV-1 for the SARS epidemic and MERS-CoV-2, for the Middle Eastern Respiratory Syndrome epidemic—that these viruses are capable of directly infecting the olfactory nerve,” explains Rowan. “Our suspicion is that SARS-CoV-2 works essentially the same way.”

Could these effects be permanent?
As their health improves, most people with COVID-19 do regain their ability to smell and taste. However, a significant proportion of patients don’t get these senses back immediately after recovery, and doctors aren’t sure if they ever will.

Part of this is because the pandemic hasn’t been around long enough, and no one knows if these patients will regain their lost olfactory senses over time. “If we chatted a year from now, we’d have a much better idea of how those statistics will play out,” Rowan explains.

But it’s likely that some people may very well be facing a long-term loss. “It’s possible to lose your sense of smell permanently after being sick with a virus,” he says. “Though relatively uncommon, it’s a top cause of anosmia among the general population.”

For those potentially looking at long-term losses, treatment is important. Various medical treatments for COVID-19-related anosmia are being examined, but as of now there is not enough research to show their effectiveness.

Instead, says Rowan, “what we have found to be the most successful for treating patients with loss of sense of smell is something called smell training.” During smell training—also called olfactory training or olfactory rehab—a healthcare provider (HCP) typically asks you to sniff different scents a few times daily to strengthen the function of your olfactory nerves.

“Just like if you had a knee surgery and needed to undergo physical rehabilitation, it's not like you lost your leg,” says Rowan. “You can still use it, but it will take some time to recover.”

Know when to seek help
How can you tell for sure if you lose your sense of smell? Rowan says there are at-home tests currently in development “to investigate this exact question.” In the meantime, he suggests taking a whiff of (nontoxic) household products to gauge yourself. (Think air freshener or soap.) Then, “ask somebody who's around you—a friend or a family member—if they can smell that same substance.”

If smell or taste has disappeared, the CDC recommends reaching out to an HCP. It may be an early sign of COVID-19, and diagnosis is important to slowing the spread of the disease.

“Just a simple call to your primary care physician is something that's very important,” Rowan explains. Screening to determine whether you should be tested for COVID-19 can be completed almost entirely through a telemedicine appointment, he adds.

“In order to not put HCPs and other patients and the rest of the world at risk, physical distancing is really important,” he says. “But it doesn't mean that you shouldn't be seeking care and does not mean that excellent care cannot be delivered.”

Ultimately, says Rowan, in the setting of a global pandemic, loss of smell and taste is something to be taken very seriously. And if that loss persists even after your recover from COVID-19, treatment is available. “If you lose it,” he says, “it doesn't necessarily mean that it's gone forever.”

Medically reviewed June 2020.

Sources:

Emily Kwong. “Is This Real? Loss of Smell And The Coronavirus.” NPR. April 1, 2020.
MS Xydakis, P Dehgani-Mobaraki, et al. “Smell and taste dysfunction in patients with COVID-19.” The Lancet. April 15, 2020.
Angela Fritz, Michael Brice-Saddler, and Maura Judkis. “CDC confirms six coronavirus symptoms showing up in patients over and over.” Washington Post. April 27, 2020.
Centers for Disease Control and Prevention. “Symptoms of Coronavirus.”
ST Moein, SMR Hashemian, et al. “Smell dysfunction: a biomarker for COVID-19 [published online ahead of print, 2020 Apr 17].” International Forum of Allergy & Rhinology. 2020;10.1002/alr.22587.
Jennifer Huber. “How viruses like the coronavirus can steal our sense of smell.” Stanford Medicine: Scope 10K. April 17, 2020.
C Hopkins, B Kumar, P Surda. “Presentation of new onset anosmia during the COVID-19 pandemic.” Rhinology. April 2020.
CH Yan. F Faraji, et al. “Self‐reported olfactory loss associates with outpatient clinical course in COVID‐19.” International Forum of Allergy & Rhinology. April 24, 2020.
Scott LaFee. “Loss of Smell Associated with Milder Clinical Course in COVID-19.” UC San Diego Health. April 27, 2020.
Allen M. Seiden. “Postviral Olfactory Loss.” Otolaryngologic Clinics of North America. 2004 Dec;37(6):1159-66.
Fifth Sense UK. “Post-Viral Olfactory Loss,” “Smell Training.”
Arnoud Cornelissen. “Aroma and taste test for Corona at home.” Innovation Origins. May 4, 2020.
Sandee LaMotte. “Loss of smell from coronavirus: How to test your sense. CNN.com. April 3, 2020.
National Institutes of Health. “COVID-19 Treatment Guidelines: Pharmacologic Interventions.”
AbScent.org. “Smell Training.”

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