Why You Should Never Eat Shiitake Mushrooms Raw

There's an old joke about mushrooms: Every mushroom is edible, but some are only edible once. While mushrooms have a wide array of culinary, medical, and, erm, recreational uses, there are some you should never, ever put in your mouth. Even some of the mushrooms you can safely eat have certain rules. Take ink cap mushrooms, which are delicious but become poisonous if alcohol is consumed three days before or after eating them. Or take shiitake mushrooms, which are also delicious, but in rare cases may give you a nasty rash if you eat them raw.

The name of the edible fungus consists of two Japanese words — "shiia," which refers to the kind of tree it grows on, and "take," the word for mushroom. They are a mainstay of soups, stir fries, and other East Asian dishes, and can be used for making a savory mushroom broth. You can also use them to make these delicious umami garlic noodles. But it's very important to cook them before eating them; consuming them raw, or even just undercooked, could give you shiitake flagellate dermatitis – a painful and itchy rash.

If you eat raw shiitake mushrooms and are affected by flagellate dermatitis, the intensely itchy rash can look rather like you were repeatedly scratched by a very angry cat. And in fact, the "flagellate" part of the name gives another clue as to how it looks: whip-like. The reaction is thought to come from a substance in the mushrooms called lentinan, which some people react adversely to. It is neutralized once the mushrooms are thoroughly cooked to an internal temperature of 293 degrees Fahrenheit. 

The good news if you develop the rash is that it's temporary, and usually goes away after a couple of weeks. And true, it may only occur in around 2% of people who eat the raw or undercooked mushrooms. But why take a chance? If you really want a raw mushroom of some kind, you can just get cremini or button mushrooms from the supermarket. Better yet, perhaps learn how restaurants make their mushrooms so delicious and find a way to cook them (thoroughly) in that particular style.