Some coronavirus patients lose their sense of smell for 30-plus days — and may never regain it. Scientists are beginning to understand why.
A resident of the Argentine Altos de San Lorenzo is performing an odor test on May 24, 2020 to monitor the loss of odor.
Alejandro Pagni / AFP / Getty Images
Many coronavirus patients lose their sense of taste and smell - according to the CDC, this is a relatively common symptom of COVID-19.
Short-term loss of smell can be due to the "cleft syndrome", in which swelling prevents flavors from reaching the olfactory neurons.
However, in patients with aggressive immune responses, these neurons can be directly damaged, so they have no sense of smell for 30 days or more.
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Kelsey Meeks sprayed a pine-scented air freshener in her office last week - and then started crying. For the first time in months, she could smell it.
Meeks, a 36-year-old lawyer who lives outside of New Orleans, Louisiana, has been suffering from the corona virus since March 30. Within a week of the onset of the disease, she noticed that her taste and smell had disappeared. Her floral, fruity perfume seemed odorless. The Tom Yum soup that she made with fresh Thai chilies had no taste.
Almost three months later, Meeks said she could tell if something was salty or sweet, or maybe smell a bit of a bad smell, but for the most part her senses are still gone.
"Before COVID-19, my ability to smell and taste was equivalent to an action film in a Dolby Atmos theater," she told Business Insider. "Now I'm looking at black and white photos instead of watching an HD movie."
Scientists are beginning to understand why the virus has this effect: In a recent article in The Conversation, Dr. Jane Parker, Professor of Taste Chemistry at the University of Reading, and Dr. Simon Gane, Rhinologist at the University of London, Dr. , explained that coronavirus patients may have a "cleft syndrome". Then swollen tissue and mucus block the olfactory cleft - the part of the nose that is responsible for the smell.
In these cases, flavors cannot reach olfactory neurons. As soon as a patient's swelling subsides, the path to his olfactory neurons opens and he should start to smell again a week or two later. However, a more aggressive inflammatory response can result in tissue damage and leave patients without a sense of smell for 30 days or more.
Patients with more severe infections may take longer to restore their sense of smell
The coronavirus penetrates the body by binding to cell receptors called ACE2. Research suggests that people with more ACE2 receptors are at higher risk of serious coronavirus infection.
Because ACE2 receptors are found in the nose, throat, intestine, lungs and heart, scientists initially thought that the coronavirus could use these receptors to destroy olfactory neurons.
Kelsey Meeks with her boyfriend on February 20, 2020 in Paris.
In an article that is still awaiting peer review, a group of researchers from the UK and US found that this was not the case. Instead, the virus appears to invade nearby cells that support the olfactory neurons. Damage to these cells leads to swelling of the nose, which can affect a patient's sense of smell - even if that person is not constipated.
In severe cases, the body's immune response can also cause it to attack healthy tissue. This can directly damage the olfactory neurons. The more aggressive the immune response, the more severe the damage can be. In some cases, some loss of smell can be permanent.
Danger of permanent loss of smell
The U.S. Centers for Disease Control and Prevention cite loss of taste and smell as a COVID-19 symptom, but it is still unclear how often it occurs. An April study of more than 200 coronavirus patients at the Wuhan, China hospital found that only 5% had taste and odor loss. However, another study with 50 coronavirus patients in the same month showed that 98% had at least some "odor disorder".
The reality is probably somewhere in the middle: A review in May found that around 53% of coronavirus patients had an olfactory disorder. A Spanish case study also found that almost 40% of patients with COVID-19 developed olfactory and / or taste disorders, compared to only 12% of those with flu.
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Crystal Cox / Business Insider
Scientists are still unsure whether the loss of smell will cause coronavirus patients to have taste problems because the two senses are closely related, or whether the virus also affects the taste buds.
Some coronavirus patients may start to regain their sense of smell if their olfactory neurons regenerate over the course of weeks or months. These patients often develop "parosmia" - a distorted sense of smell - when they recover, which can turn otherwise pleasant flavors into bad smells like chemicals or burning.
"I don't wear perfume anymore because it's just too depressing to spray on every morning and I can't smell it," said Meeks. "Sometimes I can feel a hint of it, but the part I can smell now smells horrible."
Some patients may experience permanent loss of smell if their olfactory neurons are destroyed. In these cases, there is evidence that exercise such as inhaling essential oils daily could help people regain some of their senses.
Meeks said she appreciates the little victories when it comes to regaining her sense of smell - but the idea of missing out on the joys of eating, especially in a culinary city like New Orleans, has taken a mental toll.
"The impact of not being able to experience these things gives the impression that I have suffered a much greater loss than just my senses," said Meeks. "It is a reminder several times a day that I had COVID-19 and that I still have it."
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