Still struggling with your sense of smell after battling Covid-19? You are far from alone.
A new analysis shows that about 5% of patients with confirmed cases of Covid-19 – about 27 million people worldwide – have experienced a long-term loss of smell or taste.
In an analysis published Wednesday in The BMJ (the peer-reviewed medical journal of the British Medical Association)., The researchers evaluated 18 previous studies on smell and taste loss in several continents and different demographic groups. Three-quarters of those with loss of taste or smell recovered within 30 days.
Recovery rates improved over time, but about 5% of people reported “persistent dysfunction” six months after contracting Covid-19.
The analysis suggests that loss of smell and taste may be a long-standing concern that requires more research and health care resources for patients struggling with long-term symptoms.
Loss of smell has been linked to higher mortality rates in the elderly and has a major impact on people’s emotional and psychological well-being, said Dr. Zara Patel, a rhinologist at Stanford University, was not involved in the BMJ study.
“Now that millions of people around the world have reduced sense of smell, this could be a new public health crisis,” Patel said.
Loss of smell was one of the most obvious symptoms of Covid-19 at the start of the pandemic.
“You can track a pandemic around the world,” Patel said.
The BMJ analysis provides a comprehensive overview of odor research worldwide and over time. Data from nearly 3,700 patients were included in the analysis.
Studies from North America, Europe and Asia were included in the analysis and found that women were less likely than men to recover their senses of smell and taste. Patients with more nasal congestion were less likely to recover.
The analysis showed a steady increase in the proportion of patients who regained their sense of smell over time. After 30 days, approximately 74% of patients had recovered; After 90 days, this number reached 90%. After six months, about 96% of patients reported that their smell had returned.
Scientists are beginning to understand how Covid-19 affects olfactory function.
The coronavirus often infects the olfactory bulb, which is the swelling of the passages in the upper part of the nasal cavity. where people perceive the sense of smell and process taste in addition to basic tastes such as sour or bitter.
Scientists think the virus doesn’t initially infect olfactory neurons, but instead attaches to supporting cells that provide a pathway for the neurons to signal.
Patients who lose their sense of smell after Covid-19 form a unique group, said Dr. Aria Jafari, a rhinologist at the UW Medicine Sinus Center in Seattle, was not involved in the new analysis. “They get better faster, based on the cells that are affected.”
According to Jafari, about half of his patients who have lost their sense of smell have had Covid-19 at some point. Many have had a significant impact on their well-being due to the loss.
“They are distracted by losing their sense of smell. It’s a very important part of our daily routine and what makes us human,” Jafari said, adding that he treats professional chefs, chocolatiers and others whose livelihoods depend on their ability to detect smell and taste. “What I hear most is that it leads to social isolation and disconnection from the world and society as they know it. And that can be really disturbing.”
According to Jafari, many patients describe the transition as “can be distressing” because they smell things that aren’t there, or smell things like rubber or smoke, or smell abnormal odors.
People who can’t smell or taste are more likely to have psychiatric disorders, depression and anxiety, Jafari said. In an emergency, Jafari said he treated a malnourished patient after losing his sense of smell and taste.
Smell is fundamental to how we relate to each other and our way through the world, dictating “the first impressions you make about other people, the people we choose for sex or for lifelong partners,” Patel said. Research shows that scent cues can subconsciously influence people’s attraction to others, based on their genetics.
The analysis relies on studies using self-reported data from patients. According to Patel, this may bias the results of some studies, underestimating the true effects of smell impairment, because people sometimes don’t realize how much they have lost their sense of smell.
The study’s authors agreed.
“Many previous studies have shown that objective smell testing is more helpful in identifying people with smell loss than when we ask them to self-report,” wrote Professor Song Tar Toh, study author and chair and head of the department of otolaryngology. Neck Surgery at Singapore General Hospital, via email. “The actual number of people affected may be much higher than our estimate.”
Patel suspects that the true rate of olfactory dysfunction among those exposed to Covid-19 may be higher than 20%. Perhaps women do not struggle with recovery, but are more aware of long-term olfactory deficits.
“In general, women have a stronger sense of smell than men,” Patel said. “We found that people with stronger senses of smell and taste perceive a loss and care for the loss.”
According to Jafari, the BMJ analysis generally tracks his clinical experience and patient recovery.
“It’s good to collect data from around the world to get a better understanding of what’s going on and to get some of the variability in these assays that is patient or facility specific,” Jafari said. “This generally increases the level of evidence to support what we as sinus surgeons see in our offices.”
Early versions of the Omicron variant appear to have had less of an effect on the sense of smell than previous waves of Covid-19, Patel said.
But the last subvariant BA.5 may reverse this trend.
“We don’t have enough information to know for sure,” Patel said. “I’m at my clinic now, and I’m starting to see a rebound.”
Treatment is available for people who have lost their sense of taste and smell due to Covid-19.
Structured olfactory training—patients can train the brain to recognize different odors by inhaling essential oils like lemon, clove, eucalyptus, and rose twice a day to stimulate different types of neurons. Doctors often prescribe sinus steroid rinses to reduce inflammation and help with exercise.
Some emerging evidence suggests that omega 3 fatty acid supplementation may be beneficial for patients with olfactory dysfunction.
Patel and others are investigating other treatments, including nasal injections of platelet-rich plasma and electrical stimulation.
Patel said he hopes to continue funding research and public interest in smell and taste dysfunction so researchers can dive deeper and discover new treatments.
Before the pandemic, “it was an orphan, Cinderella feeling,” Patel said. “It wasn’t until so many millions of people were injured or their loved ones were injured that people began to realize the enormous impact that smell and taste can have on your life.”