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CDC Touts Smell Training After Covid, But Results Are Unproven

June 2, 2021, 9:36 AM

Regular sniffing of lemon, clove and other spices won’t help everyone regain their sense of smell after Covid-19, but the Centers for Disease Control & Prevention says “smell training” is something people should absolutely try.

Dr. John Brooks, the CDC’s chief medical officer for the agency’s Covid-19 emergency response, first touted its use at a congressional hearing last month saying it’s a treatment that “really works.”

“I will tell you that part of the reason I wanted to emphasize that it really works is to raise people’s awareness that it exists,” he said.

But some doctors and scientists worry that may be giving people a false sense of hope about the effectiveness of olfactory, or smell, training.

“It’s perfectly safe to try, but I don’t think it’s responsible for us as scientists or physicians to say it will work in all instances,” said Steven Munger, director of the Center for Smell and Taste at the University of Florida. “We need to be cautious.”

In an interview with Bloomberg Law on May 27, Brooks said the CDC doesn’t need to recommend smell training because it’s already recommended by the professional societies like the American Academy of Otolaryngology–Head and Neck Surgery.

If people are worried the CDC is overpromising, he said they may have a different worldview that sees a glass as half empty rather than half full.

“I don’t believe that a false sense of hope is a reason to withhold making sure people know that it is available,” he said. “What I would recommend though is persons who are interested in having their smell evaluated and pursuing it should do so in the care of an expert in that area, usually that’s an ear, nose, and throat doctor.”

Brooks apologized if his comments at the April 28 hearing “came off as sort of unbridled enthusiasm.” He wanted to state publicly that a low-cost treatment exists that most people are unaware of.

Preliminary studies show some people have had success with smell training, but doctors and scientists are careful to note that it doesn’t work for everyone. It’s unclear if those who see improvement are spontaneously recovering on their own or if the treatment is really working.

Public Health Crisis

Smell training is easy, cheap, and can be done at home. Kits of scented essential oils can be purchased online, or people can make their own kits using spices, candles, and even scented soaps. The training involves repeatedly taking short sniffs of the same four scents twice daily, spending several seconds on each scent before moving to the next one. Those scents are often rose, lemon, clove, and eucalyptus.

Karen Calloway has been doing smell training since February, but she hasn’t had much success.

“I’m trying anything and everything, but nothing is really happening,” said the 58-year-old from Matawan, N.J., who lost her sense of smell completely when she caught Covid-19 at the end of April 2020. She now has parosmia, a condition that distorts her sense of smell and makes everything smell like a sweet chemical.

Calloway bought a smell kit online through AbScent, a charity in England and Wales that supports people who have experienced smell loss, and endorses and instructs people in smell training.

People make a lot of mistakes with smell training and if they don’t have an optimum experience, they give up, said Chrissi Kelly, AbScent’s founder.

“Smell training has to go on for a daily basis for about four months,” she said. “There is a mindfulness component, an engagement of the brain that’s necessary and involves calling up memories and engaging in emotions.”

Calloway admits she’s been doing smell training less lately.

“I get so discouraged now,” she said.

The use of smell training was first studied by Dr. Thomas Hummel, a doctor and professor at the University of Dresden in Germany, with a few colleagues in 2009. The study, published in the medical journal The Laryngoscope, was inconclusive. It showed 28% of the 36 participants improved with olfactory training and one out of 16 participants in a control group that did nothing recovered spontaneously. A 2013 study had better results, with 68% of people with upper respiratory tract infections who did the training showing improvement compared with 33% in the control group.

Viruses, including common colds or the flu, as well as environmental factors can cause a loss of smell, known as anosmia, or a diminished sense of smell, known as hyposmia. About 50% of people who get Covid-19 end up with some sort of smell dysfunction as a symptom of the virus, said Dr. Jay Piccirillo, a professor of otolaryngology and vice chair of research at the Washington University School of Medicine in St. Louis.

Doctors and researchers believe the Covid-19 virus, SARS-CoV-2, attacks the cells that support the olfactory nerves in the nose. About 90% of people will get their sense of smell back as they recover from Covid-19, but as many as 10% may not, Piccirillo said.

By this fall, he estimates as many as 6 million Americans could have chronic olfactory dysfunction from Covid-19.

The U.S. National Health and Nutrition Examination Survey in 2014 found over 13 million Americans have some sort of smell dysfunction. The study showed it was more prevalent among older people, but Piccirillo said Covid-19 has been impacting younger people “who, if it is permanent, will be living the rest of their lives with this olfactory dysfunction.”

“That’s a huge problem,” he said.

Can’t Hurt?

Doctors recommend smell training because there’s no risk in trying it, as long as people aren’t sniffing bleach or other chemicals that can harm your lungs.

Monique Moss thinks smell training might be helping her. The 28-year-old from Fort Wayne, Ind., started a regimen in March. She lost her sense of smell for about six months after she got Covid-19 in August 2020 and then everything started smelling and tasting like bleach. Now “everything smells like stale cigarette smoke,” she said, noting she’s never been a smoker.

“It’s like your brain is trying to tell your nose what you’re smelling, but it’s distorted,” she said. “Some days you feel like you’re making progress and other days you feel like you’ve gone 10 steps back, so it fluctuates pretty heavy.”

There is evidence from other post-viral olfactory loss patients that shows recovery takes up to three years, said Pamela Dalton, an olfactory scientist at the Monell Chemical Senses Center, a nonprofit scientific institute in Philadelphia.

Dalton recommends people try smell training, but she said it doesn’t work for everyone. Scientists still don’t know why smell training works for some people and therefore can’t predict when it’ll work, she said, but it’s better than waiting for your smell to come back on its own.

“I don’t want people to be discouraged, but I also want to give them something that has shown some promise,” she said. “It’s not for everyone.”

“Really, we have nothing else to offer you,” she added.

Other Treatments Far Away

Stem cell replacement surgeries and gene therapies are potential treatment options being studied now, but Munger said it’ll be at least a decade before those come to market and they’re likely to be costly at first.

The budding treatments are envisioned to work like gene therapy for retinal disease. The Food and Drug Administration approved Spark Therapeutics Inc.’s Luxturna as the first such treatment for a rare inherited form of blindness in 2018. It costs $425,000 per eye.

Drugs or biologic therapies may also be an option, but in all these cases Munger said the big challenge is understanding why viruses like Covid-19 are causing the smell dysfunction to start with.

In the meantime, scientists and doctors say more funding needs to be devoted to studying the effectiveness of smell training and other treatment options. The Washington University School of Medicine has two clinical trials underway now, one measuring the effectiveness of smell training both with and without an added visual component, and the other measuring the effectiveness of Theophylline, a drug used to treat respiratory diseases and asthma.

For now, Piccirillo said there is no proven effective treatment for loss of smell, so why not try smell training. “It doesn’t cost much and it won’t hurt you,” he said.

The CDC is expected to release interim guidelines in the near future to help physicians better treat people with lingering symptoms of Covid-19. If smell training is not presently in the interim guidelines, Brooks said he’s almost certain it will be the future.

To contact the reporter on this story: Lydia Wheeler in Washington at

To contact the editors responsible for this story: Fawn Johnson at; Karl Hardy at