Temporary loss of smell, known as anosmia, is a commonly reported indicator of COVID-19.
Losing your sense of smell and taste can be jarring and emotional, and adjusting to the seemingly muted world can be difficult at first. However, research looks promising for COVID-19 patients with anosmia, though scientists say there's still a lot unknown.
Here's what we know about anosmia related to COVID-19 thus far:
How does it happen?
The novel coronavirus likely changes the sense of smell in patients not by directly infecting neurons, but by affecting the function of supporting cells, said Sandeep Robert Datta, MD, PhD, associate professor of neurobiology at Boston-based Harvard Medical School. Dr. Datta co-authored a study published July 31 in Science Advances, and its findings identify the olfactory cell types in the upper nasal cavity as most vulnerable to SARS-CoV-2 infection.
Justin Turner, MD, PhD, associate professor of Otolaryngology-Head and Neck Surgery and medical director of Nashville-based Vanderbilt University Medical Center's Smell and Taste Center, said May 21 that the primary cause of smell loss appears to be from an inflammatory reaction inside the nose that can lead to a loss of the olfactory neurons.
Who loses their smell?
Smell loss can be one of the first or only signs of disease and may precede symptoms such as cough and fever, Dr. Turner said, citing spring data from VUMC's Smell and Taste Center.
A study published Jan. 5 in the Journal of Internal Medicine found that 86 percent of patients with mild COVID-19 cases experienced anosmia, compared with 4 percent to 7 percent of those with moderate to severe cases. The research analyzed data from 2,581 patients in France, Belgium and Italy.
Will COVID-19 patients get their sense of smell back?
Of 2,581 COVID-19 patients studied, 95 percent of patients regained their sense of smell within six months, according to the study in the Journal of Internal Medicine.
For most patients, COVID-19 infection is unlikely to permanently damage olfactory neural circuits and lead to persistent anosmia, Dr. Datta said, adding, "Once the infection clears, olfactory neurons don't appear to need to be replaced or rebuilt from scratch. But we need more data and a better understanding of the underlying mechanisms to confirm this conclusion."
If so, when do COVID-19 patients get their sense of smell back?
The average time of olfactory dysfunction reported by patients was 21.6 days, according to the study in the Journal of Internal Medicine. Nearly a quarter of the 2,581 COVID-19 patients studied didn't regain smell and taste within 60 days of infection.
Persistent loss of smell linked to a COVID-19 diagnosis has an excellent prognosis of nearly complete recovery at one year, according to study findings published June 24 by JAMA Network Open.
Are there any long-term physical or psychological risks?
"If you have a gas leak, you can't necessarily smell it," Nina Shapiro, MD, a pediatric head and neck surgeon at University of California, Los Angeles School of Medicine, told NBC News. "And if people lose their appetites because food tastes like cardboard or even rotting meat, they might develop vitamin deficiencies. What's more, people might not know when food is, indeed, spoiled or burning."
"Anosmia seems like a curious phenomenon, but it can be devastating for the small fraction of people in whom it's persistent," Dr. Datta said. "It can have serious psychological consequences and could be a major public health problem if we have a growing population with permanent loss of smell."