A 72-year-old man had to be treated in the emergency room at the University Hospital of Geneva (Switzerland) after suffering a strong skin reaction from eating shiitake mushrooms that were not properly cooked.

The victim arrived at the hospital with a rare rash on the skin of his back and buttocks. His skin was covered in elongated red whiplash-like lesions, technically known as flagellate erythema. The rash had started two days before and the itching, as he explained to the doctors, was so intense that it prevented him from sleeping.

They asked him what he had done and eaten in the previous days to try to find out what could have caused the reaction. He said that two days before the onset of symptoms, and four days before going to the hospital, he had prepared himself a meal that contained shiitake mushrooms, among other ingredients.

It was the key data that allowed the diagnosis to be made. The man suffered from shiitake dermatitis, a pathology first described in Japan in 1977. Although the majority of known cases have been described in East Asia, where shiitake originate, the number of cases is expected to increase. affected in the rest of the world as consumption of the mushroom spreads.

As it is not a notifiable disease, there is no record of the number of cases that occur in Europe. A study by the French Poison Control Centers identified fifteen cases in the country between 2000 and 2013, when shiitake consumption was not as widespread as it is now.

Once the diagnosis was made, the doctors at the Geneva hospital reassured the patient. Based on the experience of cases described in Asia, shiitake dermatitis is annoying but not serious. It does not significantly affect any internal organs and the symptoms usually resolve in less than two weeks, although there is a minority of patients in whom they last more than a month.

The doctors prescribed a cream with corticosteroids and antihistamine pills to relieve the symptoms, as explained in The New England Journal of Medicine, where this week they presented the details of the case.

They also advised him to make sure to cook the shiitake well from now on. Almost all of the cases described in Asia have occurred in people who had eaten raw or undercooked mushrooms. The skin reaction is attributed to lentinan, a molecule present in shiitake that is destroyed by cooking.

At a follow-up visit two weeks later, the patient said the itching had disappeared, although he had some residual reddish spots on his back.