Led by the National Institutes of Health's RECOVER initiative and supported by its Clinical Science Core at NYU Langone Health, a team of researchers from across the country explored a link between the coronavirus that causes COVID-19 and hyposmia -- the reduced ability to smell.

The results revealed that 80% of participants who reported a change in their smelling ability after having COVID-19 earned low scores on a clinical scent-detection test taken about two years later. Of this group, 23% were severely impaired or had entirely lost their sense of smell.

Notably, 66% of infected participants who did not notice any smelling issues scored abnormally low on the evaluation as well, the authors say.

"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," said study co-lead author Leora Horwitz, MD.

Horwitz, a professor in the Departments of Population Health and Medicine at NYU Grossman School of Medicine, adds that 60% of uninfected participants who did not report olfactory problems also tested poorly during the clinical evaluation.

Hyposmia has long been connected to weight loss, reduced quality of life, and depression, among other concerns. Those with a diminished sense of smell may also struggle to detect dangers such as spoiled food, gas leaks, and smoke, experts say. In addition, scientists have flagged smelling dysfunction as an early sign of certain neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease, which can affect the brain's scent-processing region.

While past research has identified hyposmia as a symptom of coronavirus infection, most of these studies have relied on patients' own assessments of their smelling ability. Such subjective measures are not always reliable and cannot effectively track the problem's severity and persistence, notes Horwitz.

The new study in 3,535 men and women, publishing online Sept. 25 in the journal JAMA Network Open, is the largest to date to examine loss of smell after COVID-19 by using a formal test, the authors say.

Along with Horwitz, Jacqueline Becker, PhD at Icahn School of Medicine at Mount Sinai in New York is co-lead author. Hassan Ashktorab, PhD, at Howard University in Washington, D.C.; Andrea Foulkes, ScD, at Massachusetts General Hospital in Boston; and Joyce Lee-Iannotti, MD, at the University of Arizona in Phoenix, are study co-senior authors.

For the investigation, the research team assessed thousands of Americans who had participated in the RECOVER adult study, a multicenter analysis designed to shed light on the long-term health effects of the coronavirus. Throughout the study, those with and without a history of COVID-19 completed surveys about their symptoms every 90 days from October 2021 through June 2025.

To measure olfactory function, the team used a clinical tool: the University of Pennsylvania Smell Identification Test (UPSIT). In this scratch-and-sniff evaluation, which is considered the gold standard of its kind, participants were asked to identify 40 scents by selecting the right multiple-choice option for each odor. A correct answer earned one point, and the total UPSIT score was compared with a database of thousands of healthy volunteers of the same sex and as. Based on the results, smelling ability was characterized as normal, mildly impaired, moderately impaired, severely impaired, or lost altogether.

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

Experts are now exploring ways to restore smelling ability after having COVID-19, such as vitamin A supplementation and olfactory training to "rewire" the brain's response to odors. Having a deeper understanding of how the coronavirus affects the brain's sensory and cognitive systems may help refine these therapies, notes Horwitz.

Horwitz cautions that the study team did not directly assess loss of taste, which often accompanies problems with smell. In addition, it is possible that some uninfected participants were misclassified due to the lack of universal testing for the virus. This may help explain the surprisingly high rate of hyposmia identified in those without a supposed history of COVID-19, she says.

Funding for the study was provided by National Institutes of Health grants R01HL162373, U01DC019579, OT2HL161847, OT2HL161841, and OT2HL156812.

Other NYU Langone researchers involved in the study are Gabrielle Maranga, MPH, and Jennifer Frontera, MD.

Other study authors are Alexander Charney, MD, PhD, and Juan Wisnivesky, MD, DrPH, at the Icahn School of Medicine at Mount Sinai; Weixing Huang, MSPH, Mark Albers, MD, PhD, and Christina Sorochinsky at Massachusetts General Hospital; Dara Adams, M.D., and Jerry Krishnan, MD, PhD, at the University of Illinois Chicago; Sarah Donohue, PhD, MPH, at the University of Illinois in Peoria; Mirna Ayache, MD, Brian D'Anza, MD, and Grace McComsey, MD, at Case Western Reserve University in Cleveland, Ohio; Jasmine Berry, MPH, Tiffany Walker, MD, and Zanthia Wiley, MD, at Emory University in Atlanta; and Hassan Brim, PhD, and Adeyinka Laiyemo, MD, at Howard University.

Additional study authors are Tanner Bryan, MS, at Denver Health in Colorado; Robert Clark, MD, Mark Goldberg, MD, and Thomas Patterson, MD, at the University of Texas at San Antonio; Melissa Cortez, DO, and Torri Metz, MD, at the University of Utah in Salt Lake City; Nathaniel Erdmann, MD, PhD, Valerie Flaherman, MD, MPH; and Emily Levitan, ScD, at the University of Alabama at Birmingham; Tamara Fong, MD, PhD; at Harvard Medical School in Boston; Jason Goldman, MD, MPH, at Providence Swedish Medical Center in Seattle; Michelle Harkins, MD, at the University of New Mexico in Albuquerque; Sally Hodder, MD, at West Virginia University in Morgantown; Vanessa Jacoby, MD, John Daniel Kelly, MD, Jeffrey Martin, MD, MPH; Megumi Okumura, MD; and Michael Peluso, MD, at the University of California San Francisco; Prasanna Jagannathan, MD, Xiaolin Jia, MD, and Andre Kumar, MD, at Stanford University in California; Kathryn McCaffrey, MD, and Helen Nguyen, DO, at the University of Washington in Seattle; Ganesh Murthy, MD, at the University of Arizona in Phoenix; Sairam Parthasarathy, MD, at the University of Arizona in Tucson; Samuel Parry, MD, at the University of Pennsylvania in Philadelphia; and Samantha Wiegand, MD, at Miami Valley Hospital in Dayton, Ohio.

Other study collaborators are RECOVER community health advocates Teresa Akintonwa, MA, and Maxwell Hornig-Rohan; and Hannah Davis at the Patient-Led Research Collaborative in New York City.