Strange But True: The Raw Shiitake Rash

Blistering red welts. A rash that spreads from the back of the hands to the neck, legs, back and abdomen. Is it poison oak? No — it’s shiitake dermatitis, a bizarre reaction to eating raw or undercooked shiitake mushrooms.

Have you ever heard of this?

More common in Asia, shiitake dermatitis is thought to be a reaction to a component of the mushroom called lentinan, which breaks down when heated. Not everyone is susceptible; in one study, only nine patients out of about 500 developed a rash after contact with lentinan. Interestingly, because the response is not triggered by the immune system, it is considered a toxic reaction rather than an allergy.

The New York Times Magazine recently ran a story about a woman diagnosed with shiitake dermatitis, alerting us to this strange condition. Although fully cooked shiitakes can be safely eaten even by those who react to lentinan, one rash was enough for her: “I’m never going to touch another shiitake.”

• Check it out: Diagnosis: A Red Scare – New York Times Magazine

Have you ever heard of anyone with this condition? Does it make you think twice about eating a raw shiitake mushroom?

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