A young woman in Italy has a rare and mysterious condition that causes her to sweat blood, according to a new report of her case.

The 21-year-old told her doctors that, over the last three years, she periodically experienced bleeding from her face and palms, without any cuts or skin lesions. These bleeding episodes typically lasted about 1 to 5 minutes and were more intense when she was under emotional stress.

While the woman was at the hospital, her doctors observed "the discharge of blood-stained fluid from her face," according to the report, which was published Oct. 23 in the Canadian Medical Association Journal. She was diagnosed with a rare condition in which blood oozes from intact skin and membranes, according to the National Institutes of Health's Genetic and Rare Diseases Information Center (GARD).

The condition has been reported for centuries, although some doctors have been skeptical of its existence, according to Dr. Jacalyn Duffin, a medical historian and hematologist at Queen's University in Kingston, Ontario, who wrote a commentary accompanying the case report. [27 Oddest Medical Cases]

But after conducting a review of recent cases of hematohidrosis — 28 cases in the last 13 years — Duffin concluded that the condition really does exist. "Credible, though scant, observations of sweating blood persist" in the medical literature, she wrote in her commentary. "This collection of well-documented observations commands respect and acceptance," she said.

However, nobody knows what causes the condition. Some researchers have hypothesized that increased pressure in blood vessels leads to the passage of blood cells through the ducts of the sweat glands, according to GARD. Others speculate the condition may be the result of activation of the body's "fight or flight" response, which generally occurs when people experience sudden fear or stress. This response triggers the release of certain hormones that make a person more alert. But in rare cases, it may also cause the rupture of small blood vessels, resulting in bleeding, according to Healthline.