Long COVID, parosmia and phantosmia: why coffee smells bad – Reuters

When a patient visited the clinic of Dr. Angela Cheung entered and said that it smelled like chicken noodle soup in here, she knew this was not possible as eating was prohibited. The patient had what is known as phantosmia, a condition in which the individual smells an odor that does not exist.

At the beginning of the pandemic, loss of smell and taste were among the most commonly reported symptoms of COVID-19. While many patients regained these senses within weeks, others took months.

For some, regaining the sense of smell was a much more difficult journey than losing it: coffee now smells like rotting vegetables, and food now smells rancid, raw sewage, smoke, or is sweet and sour.

The scent of fragrant flowers could be burnt rubber now.

These patients have what is known as parosmia, a condition in which their sense of smell is distorted. Even for people with fantasies, the olfactory hallucination is often not as pleasant as chicken soup, but a constant smell of something foul, like garbage, experts say.

“It doesn’t even smell like coffee. Things usually relax a bit over time, especially when we treat them,” Cheung, a senior scientist at the University Health Network and Sinai Health System and a leading long-COVID expert, told CTVNews.ca in an interview.

“But there are people who have very debilitating and terrible symptoms. So everything smells rotten, they can’t eat anything, everything makes you disgusting.

dr Marc Tewfik, a surgeon and associate professor of otolaryngology at McGill University Health Center, told CTVNews.ca that the smells are extremely unpleasant in most cases and can be constant in people with phantosmia.

He described it as similar to phantom limb syndrome, a common feeling amputees experience when they feel something in a limb that is no longer there. And contrary to how we can “get used” to an odor after staying in a room for a while, the odor doesn’t dissipate over time in people with phantomsmia, Tewfik said.

A study published in Nature’s Communications Medicine in May found that certain strong-smelling molecules may be the cause of most cases of parosmia and why they trigger disgust.

“It’s going to be very, very difficult for patients to deal with, and certainly I’ve seen some patients get to the point where they’re having suicidal thoughts,” he said, adding that doctors need to be careful in these types of situations . Previous research has found links between parosmia and phantosmia and patients with major depression.

“If it’s a really unpleasant smell, it’s really disgusting. And it’s relentless. After days, weeks, months it just becomes a primary part of their existence and it becomes very difficult for them.

The good news, he says, is that most of these problems develop and get better over time.


For specialists in the field, these olfactory distortions are not unique or specific to COVID-19. Although not necessarily widespread or widely discussed, parosmia and phantosmia are conditions that can occur in people with neurological disorders such as dementia, Alzheimer’s, Parkinson’s, and Huntington’s. Those undergoing cancer treatments such as radiation and chemotherapy can also get it. Environmental exposures to smoke and chemicals can also damage nerves and surface cells. Head injuries and concussions, as well as other viral infections, can trigger these olfactory changes. But before the pandemic, doctors didn’t routinely test for viruses, for example.

“Due to the scale of COVID, we’re obviously seeing a lot more,” Cheung said.

Relatively little research has been done on this particular phenomenon related to COVID-19, with studies so far suggesting that between eight and 23% of patients experience some sort of change in their sense of smell and taste three months after recovery, Cheung said. His team’s research found slightly higher percentages.

The British Medical Journal (BMJ) said in an article published in April that parosmia is a common condition following the loss of smell associated with COVID-19, which often occurs about three months after initial infection on average. The article adds that many patients said they felt their symptoms were being trivialized by healthcare providers. Another article identified persistent parosmia caused by COVID-19 as an emerging symptom that deserves more attention in the literature to raise awareness.

One study found that about a third of patients who recovered from COVID-19 had ongoing problems with smell and taste disorders, while another study found that about 5% of patients still had the smell disorder after six months .

Research suggests that loss of smell and taste are less common with the Omicron variant, but Cheung says she still sees patients reporting this problem, but perhaps a little less than before. She attributes the shift to vaccinations, noting that those infected post-vaccination and then boosted seemed to have fewer problems with ongoing symptoms, with some data showing the odds ratio of a long COVID in a third of those vaccinated lies.


Experts believe that the olfactory area of ​​the nose was injured as a result of inflammation caused by COVID-19. This is usually not direct injury to the olfactory nerve itself, but to the lining of the cells around these nerves or the epithelium on the surface of the lining. There are hundreds of receptors that send messages to our brain to help identify different smells. In the event of a violation, these messages will not be sent correctly. Most people would completely lose their sense of smell, known as anosmia, or reduced senses, known as hyposmia, but would recover with no abnormal changes.

“We think that perhaps a smaller percentage of patients have actual damage to the olfactory nerve,” Tewfik said.

“When that happens, and then sometimes when the nerve is recovering or regenerating, there can be faulty connections… we think that’s actually a sign of recovery.” It means the nerves are beginning to recover, but it can go through that phase where sensations are altered.

Cheung explains that nerves don’t register properly in the brain during recovery.

In a March article in the peer-reviewed journal Foods, 84% of patients with olfactory disorders described smells as unpleasant or nauseating, with coffee, onions, and meat among the worst triggers. The researchers said that these elements share many molecules that generate distortions and have similar pathways of formation. Gentle cooking processes that don’t involve frying, broiling, grilling, or baking can help mitigate some of the distortions, they suggested.

“Coffee, onions, garlic, fried foods, eggs and (in a non-vegetarian way of life) meat are an important part of a typical weekly diet, certainly in Western cultures, and it is clear that bias and disgust could be heading towards these foods have serious effects on diet,” the authors write.


While most patients improve over time — Tewfik says around three to six months for parosmia — some have very persistent symptoms.

“Rarely do we see patients where it takes a really long time, like more than a year or two, but fortunately that’s a very small minority,” he said.

Experts say patients can retrain their senses of smell and taste, although success rates vary. Retraining means exposing them to scents they already know, like something sweet and fruity versus something spicier like garlic or onion, and training the brain to properly recognize and register the smell. For example, patients are exposed to different odors for 15 seconds twice a day.

“It’s like retraining the olfactory system, like teaching people to walk after an injury,” Cheung said. “But the nerves don’t regenerate quickly. It takes time. »

Patients are encouraged to imagine and remember the original smell when smelling an object, Tewfik added.

One case study suggested a combination of a course of corticosteroid medication, smell training, and nasal lavage for three months to help with delirium.

“It’s a very slow process, it’s something that usually doesn’t have an immediate effect,” he added.

“The reason it seems to work is because there are stem cells in the nasal cavity that can regenerate olfactory nerves, and that’s one of the few places – if not the only place – in the body where stem cells can regenerate nerve cells, so is it really that unique to the nose.

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