The loss of smell that some people with COVID-19 experience is much different from the loss of smell that sometimes accompanies a bad cold or flu, according to a small study published online Tuesday in the journal Rhinology.
When people have COVID-19, the loss of smell tends to be sudden and severe, the study found. And, unlike with the cold or flu, the symptom does not usually occur in tandem with a stuffy or runny nose. Most COVID-19 patients who lose their sense of smell continue to breathe freely through their nose.
Perhaps even more significantly, COVID-19 patients also experience a “true” loss of taste — specifically, an inability to identify bitter or sweet tastes.
These findings suggest “that there are altogether different things going on when it comes to smell and taste loss for [COVID-19] patients and people with a regular cold or flu,” says Dr. Carl Philpott, the study’s lead author and an academic surgeon at the University of East Anglia, in a released statement.
“This is very exciting because it means that smell and taste tests could be used to discriminate between COVID-19 patients and people with a regular cold or flu,” he adds. “Although such tests could not replace formal diagnostic tools such as throat swabs, they could provide an alternative when conventional tests are not available or when rapid screening is needed — particularly at the level of primary care, in emergency departments or at airports.”
Study details
The study appears to be the first to directly compare smell and taste symptoms in people with COVID-19 with those in people with upper respiratory illnesses. The inability to smell — amnosia — has become recognized as a common symptom of COVID-19 and may be experienced by as many as half of all patients who become infected with the virus.
Of course, loss of smell can also be a symptom of a bad cold or the seasonal flu. “We wanted to find out exactly what differentiates COVID-19 smell loss with the kind of smell loss you might have with a cold and blocked-up nose,” says Philpott.
For the study, Philpott and his colleagues used standardized tests to assess the smell and taste abilities of 10 COVID-19 patients (about two weeks after the onset of the infection). They then compared those results with similar assessments that had been made of 10 people with a bad cold and 10 healthy people (the “controls”).
“We found that smell loss was much more profound in the COVID-19 patients,” says Philpott. “They were less able to identify smells, and they were not able to identify bitter or sweet tastes. In fact it was this loss of true taste which seemed to be present in the COVID-19 patients compared to those with a cold.”
The patients were followed for an average of 18 days. All reported some improvement in their smell and taste by the end of that period, although only a third of the COVID-19 patients reported a complete recovery. Philpott and his colleagues write in their paper that they expect these symptoms are likely to persist in some COVID-19 patients long after they test negative for the virus. Other research has suggested that about one in 10 patients experience a long-term loss of smell or taste.
Attacks on the central nervous system
As the researchers point out, COVID-19 is believed to affect the brain and nervous system, based on some of the neurological symptoms that some patients develop.
The findings from the current smell-and-taste study seem to support that point. The olfactory (smell) receptor cells, which are located on tissue high in the nose, are connected directly to the brain.
“Our results reflect, at least to some extent, a specific involvement at the level of central nervous system in some COVID-19 patients,” says Philpott. “It is particularly interesting that COVID-19 seems to particularly affect sweet and bitter taste receptors, because they are known to play an important role in innate immunity.”
“More research is needed to see whether genetic variation in people’s bitter and sweet taste receptors might predispose them to COVID-19,” he adds, “or conversely, whether COVID-19 infection changes how these receptors function, either directly or through a cytokine storm — the over-reaction of the body’s immune system.”
A sudden loss of smell or taste is listed as a symptom of COVID-19 on the Centers for Disease Control and Prevention’s and the World Health Organization’s website. It can be one of the first symptoms of the infection. If you experience it, call your doctor and ask if you should get tested for COVID-19.
FMI: You can read the study in full on Rhinology’s website.
I wonder if the reported profound loss of smell and taste could be related to an initial SARS-CoV-19 infection of the olfactory mucosa, where the nerve cells connect with the brain. This would not explain loss of sweet / bitter et al, where the sensory cells are located on bumps [papillae] on the tongue. Listening, M Bruce Parker
Thank you Susan…..this is a forward item.
As always, Susan Perry puts important research in accessible lay terms. I rarely comment on her columns, but I read every one!
I talked to some friends last night who had Covid, and It was the loss of taste that led them to get tested. Their other symptoms were fairly mild – they are in their early 30s and athletes. But one of them couldn’t taste a thing.
I have tested positive for COVID19 and the first symptom was complete loss of taste and smell. My first cup of coffee that morning it didn’t register with me, I just thought I didnt put enough flavored creamer in. Then I got in my car to head for work and realized I couldn’t smell my perfume when I sprayed it and couldn’t taste my orange drink. It was so profound at that point I knew it had to be COVID19 and not just my allergies. I never have run fever but have had increase headache and postnasal drainage, then came a cough a few days later. After 3 weeks I still can not taste or smell but can sense sweet, salty and bitter at the back of my mouth around the tonsils, but nothing on the tip of the tongue.
Thank You for the Covid update.
Please check your spelling of medical terminology.
The loss of smell is called Anosmia not amnosia.
FYI: The loss of taste is called Ageusia.
For me the first lack of smell symptom was that I could not smell my Clorox wipes or my alcohol wipes, or bleach. But oddly compared to the article, I could taste salty and sweet and nothing much else, so I could eat an Oreo and taste the sweet but not the flavor of whatever the Oreo has peanut butter or chocolate. My sense of smell came back after about 5 days and my wipes had sent again.