London, Researchers have shown how smell loss associated with the Covid-19 infection differs from what you might typically experience with a bad cold or flu.

The main differences found are that, although Covid-19 patients also lose their sense of smell, they can breathe freely, do not tend to have a runny or blocked nose, and they cannot detect bitter or sweet tastes.

These findings, published in the journal Rhinology, lend weight to the theory that Covid-19 infects the brain and central nervous system.

"The loss of smell and taste is a prominent symptom of Covid-19, however, it is also a common symptom of having a bad cold," said study lead author Carl Philpott from the University of East Anglia in the UK.

"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," Philpott added.

The research team carried out smell and taste tests on 10 Covid-19 patients, 10 people with bad colds and a control group of 10 healthy people -- all matched for age and sex.

They wanted to see if their smell and taste test scores could help discriminate between Covid-19 patients and those with a heavy cold.

"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," Philpott said.

"So we suspected that patterns of smell loss would differ between the two groups," he added.

The researchers found that smell loss was much more profound in the Covid-19 patents.

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.

"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," the study authors wrote.

This research also shows that there are altogether different things going on when it comes to smell and taste loss for Covid-19 patients, compared to those with a bad cold.

It has previously been suggested that the Covid-19 virus affects the central nervous system, based on the neurological signs developed by some patients.

There are also similarities with SARS, which has also been reported to enter the brain, possibly via smell receptors in the nose.

"Our results reflect, at least to some extent, a specific involvement at the level of the central nervous system in some Covid-19 patients," the authors wrote.