More and more people are suffering disturbing reactions to undercooked mushrooms

A man was left looking as though he’d been repeatedly whipped across the back after he ate what should have been a pretty standard meal.

The 72-year-old patient ended up in A&E two days after preparing a dish containing shiitake mushrooms – a very popular and common ingredient.

In the 48 hours after his dinner, he developed a painful rash that was so itchy he couldn’t sleep, according to a description of the case published in The New England Journal of Medicine.

While in hospital, doctors examined his back and found that the rash had developed into streaks of red, swollen skin that looked as though he’d been brutally lashed.

Of course, plenty of fungi are poisonous and, recently, three people died after eating a lunch believed to contain lethal death cap mushrooms.

But, in this case, the man had eaten everyday lentinula edodes (to use their scientific name) that can readily be bought in a supermarket, not a dubious foraged variety.

So what happened?

Shiitake mushrooms are the second most commonly produced edible variety in the world iStock

The health experts who examined him noted that his lymph nodes weren’t swollen, which suggested he hadn’t suffered a viral or bacterial infection.

Instead, given what he’d consumed, they diagnosed him with a rare condition known as shiitake dermatitis – a reaction which presents itself via whiplash-style streaks.

Cases of the condition were first recorded in Japan in 1977 by researcher Takehiko Nakamura, who warned of a likely increase in incidences, as shiitake mushrooms continue to grow in popularity across the globe.

Having traditionally been a staple of Japanese and Chinese cuisine, the fungus is now the second most commonly produced edible mushroom in the world, according to Nakamura.

As a result, more and more cases have emerged outside of Asia, including in Europe and South America.

The dermatitis is caused by a toxic reaction to lentinan – a carbohydrate in the mushrooms which triggers the release of chemical messengers which cause inflammation.

This then causes a patient's blood vessels to dilate, enabling the unusual rash to develop, usually two to three days after a person has eaten them, Live Sciencenotes.

Lentinan decomposes when heated, which is why this reaction occurs only when people eat raw or undercooked shiitakes.

So, the good news is that lentinan – and thus shiitake mushrooms – can be safely consumed if cooked.

Left: a patient with the trademark whelts on his stomach and, right, the 72-year-old man with marks all over his backHospital Federal da Lagoa/ABD/NEJM

It’s also reassuring to know that the dermatitis generally goes away on its own without treatment. Although, patients can be prescribed anti-inflammatory medication to treat their symptoms.

In the most recent recorded case, the 72-year-old was given topical steroids for his back and oral antihistamines to take.

After two weeks, his back was less itchy, but he did have darker patches left on his skin, which is a common after-effect of inflammation.

The man was "advised to fully cook shiitake mushrooms in the future," the study's authors wrote, adding that they hoped his case would raise awareness of the condition.

They stressed: "It is important for public and healthcare professionals to be aware of this clinically-distinctive condition, which might seem alarming initially” but is, ultimately, nothing to worry about.

Still, that doesn’t stop sufferers from feeling pretty shiitake.

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