(NEXSTAR) – Some patients diagnosed with COVID-19 may experience an odd symptom: rash-like inflammation of the toes. Colloquially called “COVID toes,” not much is known about the infection and why it happens.

According to Dawn Davis, a dermatologist at the Mayo Clinic in Rochester, Minn., COVID toes mimic a well-known ailment called pernio: skin sores or bumps that appear after exposure to cold.

“COVID toes is a pernio-like reaction that we think is due to inflammation or clotting in the superficial vessels of the feet, likely due to an inflammatory response affecting the blood vessel walls or blood cells, or a combination of both,” Davis said.

Symptoms include redness, purple discoloration and “papular spots of hemorrhage,” in which blood leaks into the surrounding tissue. It can be itchy and burn, as well.

The ailment, which occurs in both adults and children, tends to last weeks and can be painful.

“Sometime itchy, often times painful,” Dr. Amy Paller, the chair of the Department of Dermatology at Northwestern University Feinberg School of Medicine, told Nexstar affiliate WGN. “These are individuals who are often without any other sign of viral infection.”

It’s not known how common COVID toes is or why it happens.

“We’ll have to find out more as this progresses,” Paller said.

What’s especially strange about COVID toes is that it often occurs weeks after the initial COVID-19 exposure. It also tends to affect people with lower body masses, as they have less supportive tissue between their digits.

While Dawn says she’s treated a handful of cases, Paller said “we are seeing [COVID toes] in unprecedented numbers during the COVID pandemic.”

Though much remains to be understood, COVID toes is a helpful diagnostic clue, hinting to physicians that an asymptomatic patient may have the virus.

“Skin is a window to underneath,” Dawn said. “It’s another clue to the possible diagnosis of COVID.”