Shiitake Dermatitis is an erythematous rash in a “whiplash-like” pattern that usually occurs within 24-48 hours of consumption of raw or undercooked shiitake mushrooms. Only about 2% of the population has this reaction.

It is hypothesized to be a toxin-type reaction to lentinan, a polysaccharide in shiitake mushrooms, which breaks down when heated. Diagnosis is clinical, with a thorough patient history and physical exam. Rash is self-limiting and usually resolves in 10 days to 3 weeks.

Although rare, Shiitake dermatitis may cause significant distress, so it is important to recognize this rash and reassure patients that it is self-limiting