Covid-19 and common colds can both impair taste and smell, but study finds big difference

Loss of smell and taste is more severe in Covid-19 patients than in patients with common colds and that could be due to the effect the coronavirus has on the brain and nervous system, British researchers reported on Wednesday.

Loss of smell and taste is a symptom of Covid-19, but patients infected with coronaviruses that cause the common cold can also lose taste and smell because of congestion. The new research, described in a letter to the editor published in the journal Rhinology, suggests that loss of taste and smell in Covid-19 patients isn’t simply due to congestion in the nose.

STAMFORD, CT - MARCH 20: A health worker explains a coronavirus (COVID-19) test before administering the it to a motorist at a drive thru testing location operated by Murphy Medical Associates at Cummings Park on March 20, 2020 in Stamford, Connecticut. "We are still at the beginning of this public health emergency and it is my goal to ramp up our testing capacity as soon as possible," said Stamford Mayor David Martin. Communities throughout the United States have begun opening drive-thru sites to test people feeling potential symptoms of COVID-19 and that have a doctor's referral. (Photo by John Moore/Getty Images)

Related article Doctors say loss of sense of smell might be Covid-19 symptom

“We know that Covid-19 behaves differently to other respiratory viruses, for example by causing the body’s immune system to over-react, known as a cytokine storm, and by affecting the nervous system,” Carl Philpott, of the University of East Anglia’s Norwich Medical School who was involved in the research, said in a news release on Wednesday.

“So we suspected that patterns of smell loss would differ between the two groups,” he said.

Philpott and his colleagues studied smell and taste function in 10 Covid-19 patients, 10 acute cold patients and 10 healthy people who served as a control group.

The researchers not only found that the smell and taste function of Covid-19 patients was significantly worse than in both the cold patients and the healthy individuals – but also the ability to detect sweet and bitter tastes was particularly impaired in Covid-19 patients.

“It is particularly interesting that Covid-19 seems to particularly affect sweet and bitter taste receptors, because these are known to play an important role in innate immunity,” Philpott said in the release.

Related article Loss of smell from coronavirus: How to test your sense

Philpott called for additional research to explore the relationship between the virus and these taste receptors.

“It was this loss of true taste which seemed to be present in the Covid-19 patients compared to those with a cold,” he said in the release.

The researchers believe that loss of taste in Covid-19 patients isn’t just more severe, but is caused by a different mechanism in the olfactory system, which is responsible for the body’s sense of smell. The researchers say their findings indicate that Covid-19 patients are experiencing a direct loss of the ability to taste, rather than an indirect loss of taste because the sense of smell is impaired.

Covid-19 can produce increased inflammation throughout the body. The researchers suggest that this inflammation can damage taste receptors. They say it is also possible that Covid-19 can affect a part of the brain stem connected to the sense of taste.

People who have lost their sense of smell are encouraged to try "smell training", which can include sniffing flowers.

Related article Many people lost their sense of smell weeks ago. They're still waiting for it to come back

Both the Covid-19 and cold patient groups in the study reported improvement in their sense of taste and smell over time, although only 30% of Covid-19 patients reported complete recovery.

The researchers say it is likely that a portion of the Covid-19 patients will experience persistent loss of taste after they clear the virus.

The research had some limitations, including the small study size. More research is needed to determine whether similar findings would emerge among a larger group of Covid-19 and cold patients.

Yet overall, Philpott and colleagues say smell and taste tests can discriminate between Covid-19 and cold patients, which means these tests could potentially be an additional screening tool for those with the novel coronavirus.

The US Centers for Disease Control and Prevention includes a “new loss of taste or smell” on its list of Covid-19 symptoms to watch for.

“What’s called anosmia, which basically means loss of smell, seems to be a symptom that a number of patients developed,” CNN Chief Medical Correspondent Dr. Sanjay Gupta told CNN anchor Alisyn Camerota on “New Day” in July.

That symptom appears to be more prevalent in mild or moderate cases of Covid-19, and tends to appear at the beginning of the illness. It may even be one of the first signs that you are sick.

CNN’s Sandee LaMotte contributed to this report.