Now, say that fast three times with your mouth full of mushrooms. Shitake toxicoderma is a very common dermatitis in Asia, especially, China, Japan and Korea. However, it is being seen more commonly in the U.S. as the popularity of shitake mushrooms increases. The rash is fairly unique, consisting of a long linear array of urticaria. The skin looks like it has been whipped with cat-o-nine tails having red raised streaks that are very pruritic. The itchy lines can last for several weeks, and typically occur within a day of eating raw or cooked shitake mushrooms.
The mechanism of rash is felt to be due to Lentinam a polysaccharide found in the mushrooms that has immune-modulating effects. In fact, Lentinan has been used for chemotherapy in the treatment of colon and gastric cancers, It seems that individuals who get the rash have a hyper-immune response. Sun exposure can act as an adjunctive factor. The rash can be treated with steroids, usually topically, but if the problem is severe, oral steroids are used.