Post-COVID smell problems? Ontario researchers investigate treatments

Researchers at Western University in London, Ont., are focusing on what they say is an understudied issue that has a major impact on quality of life: parosmia.

The disorder involves the distortion of smell, so scents that people once found pleasant – like coffee, chocolate or perfume – end up smelling disgusting to them. According to a survey led by researchers at Western University, more than half the respondents reported that parosmia has resulted in depression.

Issues with smell, or olfactory dysfunction, are common during and after COVID-19 infection, impacting between one- and two-thirds of symptomatic patients according to previous studies, the survey authors say. It’s estimated that eight to 32 per cent of people who experience issues with smell following COVID-19 infection are impacted by parosmia, which specifically involves the distortion of smell.

Despite its prevalence, researchers say literature on it is “scarce” and it is unclear how the disorder develops in the first place.

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Of the survey participants, only three per cent reported full recovery from post-COVID-19 parosmia, with a mean recovery time of over 14 months.

While the most commonly used treatment was smell training (74 per cent), the most successful treatment reported in the survey was stellate ganglion block, or SGB.

Only 16 per cent of respondents were treated with SGB but 45 per cent of them reported improvement, compared with only 10 per cent who reported improvement with smell training.

SGB involves injecting a local anesthetic into a collection of nerves in the neck.

“The stellate ganglion controls sympathetic signals to the head, neck, arms and part of the chest. Temporarily blocking these signals through an anesthetic injection could alleviate the distorted sense of smell in patients as it appears that part of the problem is in how the brain is perceiving the signal,” said lead author Dr. Leigh Sowerby.

“It’s a procedure with minimal risk and of all the strategies patients have tried, from smell training to nasal corticosteroid sprays, SGB appears to be the most effective in treating post-COVID parosmia.”

Sowerby is hoping that the study, published in The Journal of Laryngology & Otology, will bring more awareness to the disorder and lead to a clinical trial.

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“The team at St. Joseph’s Hospital is exploring the possibility of a clinical trial to evaluate Stellate ganglion blocks to treat parosmia,” Sowerby said in an email, though it is unclear when that may begin.

“Anyone suffering from this problem and interested in potential treatment is welcome to contact the team at”

The survey was conducted between September and October 2022 and resulted in 209 usable responses from adults. The vast majority, 86 per cent, were women but it is unclear if parosmia occurs more often in women or if women were simply more likely to be in the AbScent research group or the Facebook anosmia/parosmia group where the survey was shared. Most of the respondents were from the United States at 82 per cent, while eight per cent were from the U.K., three per cent were from Canada and the rest were from 11 other countries.

Half of the respondents have received at least one dose of a COVID-19 vaccine, but 80 per cent were not vaccinated at the time of their COVID-19 infection.

“Vaccinated respondents developed parosmia 88 days after infection, while unvaccinated respondents developed parosmia 124 days after infection,” the study reads.

Typically, participants experienced a loss of taste and smell about three days after their first COVID-19 symptoms, which recovered about four weeks later. Then, 12 weeks after infection, they developed parosmia.

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More than half the respondents reported depression and weight loss due to parosmia. Although not common, 2.5 per cent reported suicidal thoughts.

The top 10 triggers for parosmia are onion, garlic, meat, coffee, chicken, eggs, peanut butter, chocolate, fried foods and perfume.

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