The growing list of strange possible symptoms of COVID-19 may have another addition: "COVID tongue".
Whilst a loss of taste is a known symptom, British researcher, Tim Spector OBE, who is helping to track the warning signs, says some patients have reported developing painful mouth ulcers or rashes on their tongues.
Spector, a professor of genetic epidemiology at King’s College London and the lead investigator of the ZOE COVID Symptom Study app, has dubbed it "COVID tongue".
"COVID tongue" could be one of a whole host of "non-classic symptoms" that tend to get overlooked, including skin rashes, and changes to the palms of the hands or soles of the feet, known as "COVID toes".
"We have about four-and-a-half million who have given us their symptoms across three countries and we've over 20 symptoms of COVID now, and so we are finding rare symptoms that haven't been noticed before," said Professor Spector.
He describes COVID tongue as when "bits get taken out of it, called scalloping and you can often have a furry coating of the tongue as well, which seems to be associated with other symptoms of COVID as well, sometimes the COVID rash, but often it occurs after the first few classic symptoms".
"It was ignored by most doctors who didn't think it was related, but now with all these increasing reports, it's looking like it's part of this syndrome," he said.
"And it looks like other conditions of the tongue that get affected by viruses, and that's why it's also being called 'geographical tongue' because your tongue looks like a map of the world because of the way you have some bits that are raised and some that are lowered.
"COVID tongue is still not common. Less than one in 100 people have reported the problem, but it may become more so once people realise it's associated.
"People have been sending me pictures of their tongue and now we are asking routinely for them in our app.
"It tells me there are many different symptoms of COVID, particularly in the first few days that the medical community wasn't recognising.
"And it's really essential that if something unusual happens, something you are really not expecting, while COVID is so common in Europe people should think this could be related, and take the appropriate precautions."