The UK National Health Service (NHS) is being urged to add the "COVID tongue" to its official list of coronavirus symptoms.
More COVID-19 patients are suffering sores on their tongues and unusual mouth ulcers after contracting the virus, according to Professor Tim Spector, an epidemiologist at King's College London.
He says he's seeing a rise in the number of people with the side effect.
A high temperature, continuous cough and a loss of smell or taste are among the main symptoms of COVID-19, according to the NHS website.
But it is important to also draw attention to less common symptoms, such as skin rashes.
People may continue to spread this deadly virus if these symptoms are being unaccounted for, Prof Spector says.
"One in five people with COVID still present with less common symptoms that don't get on the official [Public Health England] list - such as skin rashes," he tweeted last Thursday.
"Seeing increasing numbers of COVID tongues and strange mouth ulcers. If you have strange symptoms or even just headache and fatigue, stay at home!"
COVID tongue refers to patches and ulcers across the mouth, especially on the tongue.
But British Dental Association spokesperson Professor Damien Walmsley told Mail Online red and white patches on the tongue can also be caused by other infections.
"The white patches usually rub off, leaving a sore red patch underneath," he said.
"It could also occur in those who have been taking antibiotics, or using asthma inhalers."