Nearly 25% of Covid-19 patients who reported losing their sense of smell said they did not regain their olfactory function even 60 days after they noticed it was gone, according to a large prospective study in the Journal of Internal Medicine—a potentially pervasive loss that providers believe could affect patients' nutrition and mental health.

An overview of recovery clinic models for Covid-19 long-haulers

Study details

For the study, Jerome Lechien of Paris Saclay University in France and colleagues assessed self-reported data from 2,581 ambulatory and hospitalized patients who had confirmed cases of SARS-Cov-2, the virus that causes Covid-19. The patients—who were identified at 18 hospitals across Europe between March 22, 2020, and June 3, 2020—answered olfactory and gustatory questions based off of the section of CDC's National Health and Nutrition Examination Survey focused on smell and taste.

Overall, about 1,916 patients said they experienced loss of smell, including about 85.9% of the 2,194 patients with mild cases of Covid-19, 4.5% of the 110 patients with moderate cases, and 6.9% of the 277 patients with severe or critical cases. After about 60 days, roughly 24% of all patients said they still hadn't recovered olfactory function.

Researchers also evaluated a smaller sample of 223 patients with objective olfactory exams— known as the Sniffin Sticks test, which consists of 16 smell pens—and found that 15.3% of participants still demonstrated some loss of smell at 60 days, and 4.7% still had not recouped their ability to smell at six months.

Ultimately, although recognizing several limitations to their study, the researchers concluded that milder cases of Covid-19 are significantly more likely to be associated with olfactory dysfunction. They hypothesized that this occurs because the inflammation spurred by those patients' more robust immune response to infection may adversely affect their olfactory cells.

The researchers said the pervasive lack of smell among Covid-19 patients demonstrates a demand for PCPs, ENT specialists, and neurologists to advise Covid-19 patients about olfactory dysfunction and the odds of recovery. "Considering both subjective and objective data," Lechien and colleagues wrote, "we may suggest that the 60-day recovery rate ranges from 75% to 85%."

Some Covid-19 patients grapple with long-term loss of smell

According to the Times, experts are particularly worried by the pervasiveness of this loss of smell among Covid-19 patients because olfactory dysfunction is linked to not only nutritional deficiencies stemming from lost appetite, but a host of mental health concerns—including social withdrawal, anxiety, depression, and anhedonia.

Of course, "the most immediate effects" of loss of smell are likely nutritional, the Times reports. People who've lost their sense of smell—although able to experience basic tastes, such as salty and sweet—also lose the enhancement and complexity that a sense of smell adds to the experience of taste, which in turn leads to a loss of appetite.

For instance, Kara VanGuilder, a medical administrator, said she's dropped 20 pounds since she lost her sense of smell in March 2020, and Katherine Hansen, a Seattle-based realtor, said since she's lost her sense of smell because of Covid-19, she can not only not taste food, but she can barely tolerate chewing it—she lives mostly on soups and shakes.

Still other Covid-19 survivors who've lost their sense of smell are plagued by foul phantom odors, the Times reports. Eric Reynolds, who lost his sense of smell when he fell ill with Covid-19 in April 2020, said he frequently perceives bad smells he knows aren't real, such as how soap smells like stagnant water or ammonia.

And among patients like Eric who do start to recover their sense of smell, it's not uncommon for them to develop food aversions linked to the phantom odors they detect—likely a side-effect of slowly recovering nose receptors misfiring signals or having signals misread by the brain. For instance, Evan Reiter, medical director of the smell and taste center at Virginia Commonweath University, who's been monitoring the recovery of about 2,000 Covid-19 patients with olfactory dysfunction, said one of his recovering patients reports that "virtually everything that she eats will give her a gasoline taste or smell."

But beyond nutrition and appetite, the mental health concerns of the condition are potentially staggering, experts added. As Sandeep Robert Datta, an associate professor of neurobiology at Harvard Medical School, explained, a sense of smell is intimately linked to memories and emotional well-being—and losing it "can be really jarring and disconcerting." He continued, "You think of it as an aesthetic bonus sense. But when someone is denied their sense of smell, it changes the way they perceive the environment and their place in the environment. People's sense of well-being declines."

And then there's just the sheer number of people potentially affected, he said. "If you think worldwide about the number of people with Covid, even if only 10 percent have a more prolonged smell loss, we're talking about potentially millions of people," Datta said.

Pamela Dalton, who researches the link between smell and emotion and cognition at Monell Chemical Senses Center, added, "Smell is not something we pay a lot of attention to until it's gone. Then people notice it, and it is pretty distressing. Nothing is quite the same."

For instance, according to British researchers who assessed the experiences of about 9,000 Covid-19 patients participating in a Facebook support group established by the charity group AbScent, many people said their loss of smell not only spurred a disinterest in eating, but also in socializing. As one user wrote, "I feel alien from myself … Like a part of me is missing, as I can no long smell and experience the emotions of everyday basic living" (George, MedPage Today, 12/23/20; Lechien et al., Journal of Internal Medicine, 1/5; Rabin, New York Times, 1/2).