PICTURE THIS: You will NEVER guess what caused these scratches

IN A regular series, we bring you fascinating pictures shared by doctors — and the stories behind them ... THESE bizarre marks aren’t scratches — they’re actually due to eating raw mushrooms.

The patient, a 50-year-old man, went to hospital with the rash a few days after attending an Asian food festival.

Some medications, such as chemotherapy drugs, can cause a similar reaction, but doctors diagnosed him with shiitake flagellate dermatitis — caused by eating raw shiitake mushrooms. These are the second most common edible mushrooms in the world, heavily used in Japanese and Chinese dishes.

They have a number of potential health benefits — research has shown they may help lower blood pressure, reduce high cholesterol and even protect against cancer, according to a 2014 report published in Polish medical journal Postepy Dermatologii I Alergologii.

However, if eaten raw, they can trigger the reaction seen here. This image was posted on Figure 1, an app and website where doctors around the world share images and canvass colleagues’ opinions.

Shiitake dermatitis, also known as flagellate dermatitis due to the whip-like marks, was first identified in 1977 by a Japanese scientist who saw several patients with the reaction after eating the mushroom.

Cases have since been documented worldwide, according a 2016 study in the American Journal of Clinical Dermatology.

The symptoms are caused by a toxic reaction to a molecule called lentinan. This breaks down upon heating, which is why only raw or partially cooked shiitake mushrooms cause a problem. Perhaps surprisingly, the reaction is not allergic, but toxic — and is thought to occur by lentinan triggering blood vessels to dilate and leak small amounts of inflammatory compounds just beneath the skin.

The rash, which is often itchy with red spots and small blisters that form in a whip-like line on the torso, arms and legs, usually begins to appear within three days of eating the mushroom and lasts anything from ten to 21 days. It is not thought to cause long-term damage.

The affected person may feel unwell or develop a fever, or have no symptoms at all. Steroids may be used to shorten the duration of the rash, and antihistamines given for the itch.

Not everyone who eats undercooked mushrooms will suffer the reaction. In one study, published in the Australasian Journal of Dermatology in 2003, 2 per cent of people exposed to lentinan developed the rash.

Heating the mushrooms to over 145c removes the risk.