More than a million people in the United States may not have regained their sense of smell months after Covid-19 infection, study estimates

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The research published in JAMA Otolaryngology-Head & Neck Surgery estimated that between 700,000 and 1.6 million people in the United States who had Covid-19 lost or had a change in their sense of smell that lasted more than 6 months. This is probably an understatement, said the authors of the University of Washington School of Medicine in St. Louis.

The study suggests that most people regain their sense of smell eventually, but some may never regain it. The authors consider this a concern because, by comparison, before the pandemic, only 13.3 million adults aged 40 and older had what scientists call olfactory dysfunction (OD) or chronic olfactory dysfunction (COD).

“These data suggest an emerging concern about OD and the urgent need for research that focuses on treatment of COVID-19 COD,” the study said.

A study last year found that 72% of people with Covid-19 regained their sense of smell after a month, but for some, it is a much slower process.

“The long-term disease burden of this, we’ve been literally dealing with this for decades,” according to John Hayes, director of the Sensory Assessment Center at Penn State College of Agricultural Sciences. Hayes did not work on that study but did research in the area.

He thinks the estimated number of people in the study with this problem is conservative and the issue could affect many millions more.

While long-term loss of sense of smell may sound insignificant compared to other symptoms of long Covid, such as chronic fatigue or heart problems, not being able to smell can be dangerous, he said. A 2014 study found that people who lost their sense of smell were more than twice as likely to experience dangers as eating spoiled food than those who had a sense of smell. Loss of sense of smell has also been linked to depression in earlier studies.

“It’s really consistent with appetite and social relationships, how people have lost their sense of smell may not be able to detect if they have a body odor, and can also affect diet,” Hayes said.

Hayes said his research with Covid-19 patients showed they experienced three different types of long-term olfactory disorders.

Some lose or have decreased sense of smell. Some have a sense of smell that is far away, where instead of flowers, for example, someone would smell foul-smelling feet. Others may have what Hayes calls a kind of “ghost limb syndrome” for sense of smell, where people smell things that aren’t actually there, like a constant chemical or burning odor.

Dr. Sandeep Robert Datta, a neurobiologist at Harvard Medical School who studied why people with Covid-19 lose their sense of smell, said this is an important line of research.

“We never really had a formal estimate of how many people struggled with this,” Datta said. “This is a truly unusual event in terms of olfactory dysfunction and an unprecedented consequence of a pandemic that has never really been observed before.”

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Unless someone breaks their nose in an accident or has had some other type of head trauma, it is unusual for younger people to lose their sense of smell, especially due to a virus. As people get older, some do lose some sense of smell. One study found 60 to 70% of people age 80 and older have some olfactory dysfunction. Other studies suggest that it may affect fewer people, but this loss usually occurs slowly over time; acute loss is unusual.
Scientists are still trying to find out why people with Covid-19 lose their sense of smell. Datta said the consensus seems to be that there is a disruption in the supporting cells in the nose. He said it is unlikely that the neurons responsible for detecting odors are directly attacked by the virus.

“After that, there’s still a lot of mystery about what’s going on and in a lot of labs, including mine, we’re still working on this problem,” Datta said.

Understanding how Covid-19 has distorted someone’s sense of smell will be important for scientists to determine how to help them recover it if it does not return on its own.

Some long Covid clinics offer a kind of physical therapy for the nose and restrain people’s sense of smell by exposing them to certain odors so that they can try to relearn them. Studies show that this may work for some people, but not all.

“I had a patient call me the other day and ask what could be done and honestly, I still don’t have good recommendations,” Hayes said.

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