‘Smell Training’ Could Help People Who Lost Their Sense of Smell From COVID-19

A new study shows that undergoing “smell training” may help some people regain their sense of smell if they lose it or it becomes distorted after an illness—including COVID-19.

For the retrospective cohort study, which was published in the journal The Laryngoscope, the researchers analyzed data on 153 patients with post‐infectious olfactory dysfunction (PIOD)—the loss of smell after an illness—who sought care at ear, nose, and throat clinics in Germany between 2008 and 2018.

The patients received a range of smell training kits with different scents, including eucalyptus, lemon, rose, cinnamon, chocolate, coffee, lavender, honey, strawberry, and thyme. They were tested at the start of the trial to see how well they could smell the different odors and then tested again after six months of smell training.

The researchers discovered “clinically relevant improvements” in overall smell function in people who had a lower sense of smell at the start of the trial. People with parosmia—a distortion of the sense of smell or loss of scent intensity—and older people were also more likely to show improvement over time.

The authors of the study concluded that smell training can lead to a “clinically relevant recovery” in a person’s ability to distinguish between scents and identify different scents.

What Causes Distortions in Smell?

There are several medical terms used to describe changes in a person’s ability to smell properly: parosmia, anosmia, hyposmia, and dysgeusia.

Parosmia is a medical term for distortions in a person’s sense of smell. A person with parosmia might be able to detect scents, but the smell of certain things—or sometimes everything— is different and usually unpleasant.

Anosmia is the loss of the ability to detect one or more smells. It can be temporary or permanent and has been listed as a major symptom of COVID-19 by both the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO).

Hyposmia occurs when a person’s ability to detect odors is reduced.

Dysgeusia is an altered sense of taste, which sometimes accompanies a change in sense of smell.

Richard L. Doty, PhD, Director of the University of Pennsylvania's Smell and Taste Center, tells Verywell that smell distortions can be caused by COVID-19 and other viral illnesses, along with head injuries.

How Smell Training Can Help

Smell training is a practice that repeatedly exposes a patient to various smells in an effort to help improve their ability to detect scents.

“It is still not fully known how smell training works, but it relies on the unique ability of the olfactory nerve to regenerate,” Benjamin S. Bleier, MD, FACS, a head and neck specialist at Mass Eye and Ear Sinus Center and an associate professor of otolaryngology-head and neck surgery at Harvard Medical School, tells Verywell.

“It is thought that repeated exposure of odors promotes the neurogenerative capacity of special cells in the region of the nose responsible for smell—the ‘olfactory epithelium’—which can help to heal damaged smell nerves,” Bleier says,

Smell training may even cause “better brain connectivity,” Thomas Hummel, MD, co-author of the study and a professor in the Smell and Taste Clinic at the Technical University of Dresden, tells Verywell Health.

With smell training, people are usually asked to smell certain scents and to try to think of what the scent should actually smell like while they’re doing it. There is some variation with smell training, though, including how often it’s done and which scents are used.

Bleier says that there isn’t a set standard based on studies. “The types of odors used differs throughout the literature, but there is evidence that it is important to pick odors from different categories such as aromatic, fruity, and floral."

Research has also followed patients who undergo smell training from anywhere between 12 to 56 weeks. Bleier adds that “there is some evidence that longer protocols produce better results.”

How Effective Is Smell Training?

It’s debatable. “We’ve done double-blind studies that show that improvement in smell over time isn’t any better than spontaneous improvement without smell training,” Doty says.

He also points out that most studies on smell training aren’t double-blind (meaning, people are aware that they’re receiving smell training in most studies) and don’t have controls to compare patients who receive smell training to those who don’t.

Bleier says that it's too early to tell if smell training will help patients who have a loss of smell or distorted sense of smell after having COVID-19. “The good news is there is no real downside or side effects from smell training, so it is certainly something patients can try as soon as they start to experience symptoms," he says.

While Doty is hesitant to say that smell training actually works, he says that some patients who visit his clinic for smell issues will try it, adding that "it doesn’t hurt."

Overall, Bleier recommends that people who are experiencing smell loss try scent training. “While many questions still exist about the best number of odors and how long to train for, we do know it is convenient and does not have any significant side effects,” says Bleier, adding that it “should be considered in any patient experiencing smell loss.”

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