Loss of Smell and COVID-19: What You Need to Know

Apr 03, 2020 2:50 PM

Author: Doug Dollemore


covid19 smell
Smelling an orange or flower is a good way to test if you have lost your sense of smell, a possible early warning sign of COVID-19 infection.

Roses are red. Violets are blue. If you can’t smell either, COVID-19 may have a hold on you.

Although it has yet to be proven, growing anecdotal evidence backed by emerging epidemiological findings suggests that anosmia—the loss of the sense of smell—could be one of the earliest telltale indicators of the viral disease in some people.

“It’s really not surprising that people lose their sense of smell when they have viral infections,” says Jeremiah Alt, MD. PhD, a University of Utah Health otolaryngologist who specializes in care of the ear, nose, and throat. “It’s generally caused by congestion and inflammation of the nasal passages. What’s curious about COVID-19 is the number of patients who are presenting with the loss of smell before they have any symptoms of upper respiratory infection. That is new. Typically, we don’t think of it that way. It is also presenting with much more severe loss of smell than we typically see.”

The prevalence of these reports has led some doctors and medical organizations to urge those who lose their sense of smell to isolate themselves for seven days, even if they have no other symptoms, in order to diminish the risk of spreading COVID-19 to others.

How Common Is it?

Overall, viral infections account for about 40% of all cases of anosmia. During the current COVID-19 pandemic, loss of the sense of smell is a common symptom in many parts of the world, including South Korea, where 30% of patients with confirmed cases reported losing their sense of smell during the course of the disease.

However, in recent weeks, more and more stories have emerged of people who lost their sense of smell first. These anecdotal stories in the media—a mother infected with coronavirus who could no longer smell her baby’s full diaper, or a man who couldn’t smell that his lawnmower was leaking gasoline—are gaining support from a few epidemiological studies. 

For instance, in one preliminary study of 417 patients conducted in four European countries, researchers concluded that one in eight of those who tested positive for COVID-19 lost their sense of smell before the onset of any other symptoms.

As a result, Alt says doctors are beginning to strongly suspect that an otherwise healthy person who loses their sense of smell could have the virus and spread it to others unknowingly.

What’s Causing It?

One common cause of anosmia is essentially mechanical. Nasal congestion and inflammation often make it hard for air to pass through the nose, making it difficult to detect odors.

But in the case of COVID-19, researchers suspect the virus could be disabling nerve cells in the nose that pass signals onto the olfactory bulb in the brain, where odors and smells are deciphered. Although the exact physiological mechanism isn’t fully understood, Alt says it’s likely that coronaviruses bind to a cell receptor called ACE2, triggering temporary—or, in some rare cases, permanent—loss of the sense of smell.

The virus could also disrupt the function of cells surrounding these nerves, according to Matthew Wachowiak, PhD, a U of U Health brain investigator and president of the Association for Chemoreception Sciences. Among these are sustentacular cells, which supply nerve cells with nutrients and maintain the ion balance they need to survive. 

“It’s very preliminary, but it looks like the virus might be infecting supporting cells that are around the olfactory neurons,” Wachowiak says. “Then, for reasons that still aren’t clear, that causes the olfactory neurons not to detect odors anymore.”

What Should You Do?

If you suspect you have lost your sense of smell, Alt suggests you test it by taking a whiff of an orange, a flower, or something with a strong pungent odor in your household. A decreased sense of smell or taste means that you are eligible for COVID-19 testing

If you have a chronic medical condition or develop high or persistent fever or difficulty breathing, you should contact your physician, urgent care, or emergency department for further instructions.

Your sense of smell should return once you have recovered, Alt says. 

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