Loss of Taste, Smell in COVID-19 Might Last Up to 5 Months

Preliminary research presented ahead of the American Academy of Neurology’s 73rd Annual Meeting suggests that loss of smell and taste—one of the most specific COVID-19 symptoms—can last for up to five months after infection.

In an American Academy of Neurology press release for the new study, author Johannes Frasnelli, MD, at the University of Quebec at Trois-Rivieres said that even though COVID-19 is a new disease, "previous research shows that most people lose their sense of smell and taste in early stages of the illness."

Indeed, an August 2020 study from the Mayo Clinic Proceedings found that 41% of people with COVID-19 experience a loss of smell and taste.

Another study in JAMA Otolaryngology-Head & Neck Surgery suggested that loss of smell and taste tends to come back when a person recovers from the infection. In the study, 49% of people recovered the senses after 4 weeks while 41% reported an improvement in their recovery.

However, the more recent study provides evidence that loss of smell and taste can be persistent symptoms. “We wanted to go further and look at how long that loss of smell and taste lingers, and how severe it is in people with COVID-19," Frasnelli added in the press release.

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New Study Tests the Senses

The study enrolled 813 healthcare workers from the Quebec National Institute of Public Health four months after they tested positive for COVID-19. Five months after they were diagnosed, the subjects were asked to complete a home test that assessed their ability to taste and smell.

Additionally, an online questionnaire asked the participants to self-report any issues with smell and taste, as well as self-rating their senses from a scale of 0 (meaning can’t smell or taste anything) to 10 (a strong sense of taste or smell).

About 71% of healthcare workers lost their sense of smell when they first tested positive for COVID-19. Five months later, 51.2% of the people in that group had not recovered their sense of smell. Based on the results of the home tests, 18.4% of the subjects showed a persistent loss of smell.

Approximately 64% reported losing their sense of taste when they had COVID-19. Five months later, 38% of the group said that they had not recovered their sense of taste.

In the study's press release, Frasnelli said that the findings showed that "an impaired sense of smell and taste may persist in a number of people with COVID-19," and that the findings show the "importance of following up with people who have been infected, and the need for further research to discover the extent of neurological problems associated with COVID-19.”

Why Does COVID-19 Cause Loss of Smell and Taste?

Loss of smell and taste is an early sign of COVID-19. Nitin Desai, MD, CEO and CMO of COVID PreCheck, tells Verywell that loss of these senses is a more robust indicator of infection than other symptoms.

“Physicians have to differentiate whether a cough is a sign of the flu or COVID," says Desai. "Is your runny nose from allergies or COVID? If loss of smell and taste is a symptom you’re experiencing, you have more reason to get tested.”

ACE2 Receptors

The SARS-CoV-2 virus acts on ACE2 receptors, which Desai says serve as a bridge for the virus to enter and infect host cells. ACE2 receptors are found in the nasal mucosa of the nose, which has an almost direct connection to the brain.

A July 2020 study published in Science Advances demonstrated that SARS-CoV-2 infects the ACE2 receptors found in the support sensory neurons of the nose called sustentacular cells, which help it register odors.

The mouth also has ACE2 receptors and our sense of taste is directly related to smell; that's why people who lose their sense of smell may also have difficulty detecting flavor.

Immune Response and The Brain

While the mechanism behind the loss of smell and taste is still unknown, Desai says that the rigorous immune response and cytokine storm could be causing collateral damage to organs.

“There are studies from spinal fluid showing abnormal proteins suggesting COVID infects multiple organs, including kidney, the heart, and the brain,” says Desai. “Everything in COVID is an acute infection, but I think some people have lingering organ damage from the immunological process causing symptoms. So, loss of smell is almost like a neurological symptom.”

Desai suspects that there is damage to brain areas involved in how we sense odors and that it could be that people do not lose the physical ability to detect scents, but rather, that their perception of scent is affected.

The damage to organs after infection with the virus can lead to the lingering effects observed in COVID long-haulers. While it’s too early to confirm if the loss of smell and taste continues after post-infection, it could be a clue as to why some patients have lasting neurological and psychiatric symptoms such as brain fog.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.