FRIDAY, Sept. 26, 2025 (HealthDay News) — A COVID-19 infection might blunt a person’s sense of smell for years afterward, but so subtly they might not even notice it, a new study says.

In all, 4 out of 5 people who reported that COVID had altered their sense of smell still scored low on a clinical scent detection test taken about two years later, researchers reported in JAMA Network Open.

In addition, two-thirds of COVID patients who didn’t notice any problems smelling as a result of their infection also scored abnormally low on the test, researchers said.

“Our findings confirm that those with a history of COVID-19 may be especially at risk for a weakened sense of smell, an issue that is already underrecognized among the general population,” co-lead researcher Dr. Leora Horwitz, a professor of population health and medicine at NYU Grossman School of Medicine in New York City, said in a news release.

A diminished or lost sense of smell is no small thing. It’s been connected to weight loss, reduced quality of life and depression, and those who can’t smell also might not be able to detect dangers like spoiled food, gas leaks or smoke, researchers said.

Problems with sense of smell also can be an early sign of brain disorders like Parkinson’s or Alzheimer’s disease, researchers noted.

For the new study, researchers studied 3,525 people, including 2,956 who’d been infected with COVID and 569 who hadn’t, who were taking part in a long-term research effort on the effects of the coronavirus.

As part of the project, participants completed surveys about their symptoms every 90 days between October 2021 and June 2025.

Researchers also asked the participants to take a gold-standard smell test, in which they were asked to identify 40 different scents from scratch-and-sniff pads.

Results show that 80% of people who’d reported that COVID altered their sense of smell still scored low on the scent identification test.

Of this group, nearly a quarter (23%) still had a sense of smell that was severely impaired or entirely lost, researchers said.

What’s more, many people who thought they’d dodged the bullet when it came to COVID and their sense of smell really hadn’t, researchers found.

About 66% of COVID patients who didn’t notice any changes in their sense of smell scored poorly on the identification test, results showed.

“These results suggest that health care providers should consider testing for loss of smell as a routine part of post-COVID care,” Horwitz said. “While patients may not notice right away, a dulled nose can have a profound impact on their mental and physical well-being.”

Horwitz also noted that 60% of people who didn’t catch COVID also performed poorly on the scent identification test. However, it’s possible that some of these folks actually had COVID but were never diagnosed, due to a lack of universal testing for the virus.

Other research efforts are now focused on ways to restore sense of smell that’s been damaged by COVID, such as vitamin A supplements or training to “rewire” the brain’s response to odors, Horwitz said.

Understanding the true causes of the coronavirus’s impact on the sensory systems of the brain might help improve these therapies, Horwitz said.

More information

The Mayo Clinic has more on COVID-19 and loss of smell.

SOURCE: NYU Langone Health, news release, Sept. 25, 2025