Some coronavirus patients may develop 'COVID tongue' - a painful rash or 'furry coating' on their swelling tongues, a researcher says

• Some people infected with the coronavirus might have "COVID tongue."
• The condition may involve a painful rash, swelling, or discoloration on patients' tongues.
• One UK researcher says it's critical to draw attention to "non-classic" coronavirus symptoms like COVID tongue that aren't on official public health lists.

As the pandemic progresses, experts are identifying more and more symptoms that could signal a coronavirus infection.

According to one researcher in the United Kingdom, "COVID tongue" should be added to that growing list.

"Seeing increasing numbers of COVID tongues and strange mouth ulcers," Tim Spector, an epidemiologist from King's College London, tweeted earlier this month.

"COVID tongue" may involve swelling, a painful rash, or indentations on the sides of their tongue.

Spector later told NBC News he's also heard about patients with a white or yellow "furry coating" on their tongues.

—Tim Spector (@timspector) January 13, 2021

More research is needed to confirm whether "COVID tongue" could be a reliable litmus test for a coronavirus infection, Spector said, adding that very few people - less than one in every 500 cases - have this symptom.

Mouth ulcers are also among symptoms that are 'frequently involved' in COVID-19 cases

Multiple studies published last fall suggest "COVID tongue" symptoms include ulcers too.

Researchers from the Czech Republic documented 26 cases of people with mild or moderate COVID-19 who developed painful ulcers on their tongues between April and June.

Ulcers are open sores, or breaks in the skin; the Czech scientists found up to seven half-a-centimeter-long ulcers on each patient, typically on the sides of the tongue. Following a prescription of antimicrobial mouthwash, the patients' ulcers disappeared after one to two weeks.

Other findings from Spain suggested that mouth and tongue-related issues are "frequently involved" in COVID-19 cases and deserve further examination.

That study, published in the British Journal of Dermatology found that one-quarter of 666 coronavirus patients who were sick with mild or moderate COVID-19 in a Madrid field hospital between April 10 and April 25 had problems with their mouths or tongues.

Some of the patients had developed rashes on top of their tongue, grooves on the sides of their tongue, or lost some of their papillae - the tiny bumps that give our tongues a rough texture and help us taste.

Others developed mouth ulcers or had their tongues swell up.

An August study from Brazil documented eight coronavirus cases that involved mouth ulcers and yellow, white, and red sores on patient's lips and gums.

'Non-classic' COVID-19 symptoms tend to get ignored

Neither the UK's National Health System nor the US Centers for Disease Control and Prevention report "COVID tongue" as a coronavirus symptom.

A sore throat and loss of taste are the only mouth-related issues listed, though the CDC says its list "does not include all possible symptoms."

But 20% of people have less common symptoms that aren't on the official list, Spector said.

"Non-classic symptoms" of COVID-19 tend to get ignored, including COVID tongue, skin rashes, and "COVID toes," he added.

Some coronavirus patients report scaly rashes on their feet and purple, swollen toes that look as if they've been frostbitten - a condition doctors have nicknamed "COVID toes."

Other patients - particularly those with long-lasting symptoms - have reported other skin problems including hives, lesions, and itchy rashes all over their bodies.

Mouth ulcers are a common symptom of other viruses like hand, foot, and mouth disease and herpes, so dentists who frequently examine people's mouths and tongues have already been on the lookout for these symptoms in their patients during the pandemic.

The American Dental Association (ADA) told NBC News that the study published in the British Journal of Dermatology aligns with what it has heard from colleagues and partners about coronavirus patients' mouth and tongue issues.

"Oral health is an important and vital part of overall health, and the ADA is continuing to examine the connection between the two as it relates to COVID-19," the association told NBC in a statement.