The Shiitake mushroom, Lentinula edodes, is a widely used culinary ingredient. There is a risk of a reaction from consuming the mushroom raw or undercooked. For individuals that are affected a rash usually manifests as a cutaneous eruption in about 2 days after ingestion. The symptoms are dark red welts over most of the body that make the patient appear to have been flogged. That is why it is sometimes referred to as “flagellate dermatitis.” The rash lasts for approximately 10 days and is not an allergic reaction but is caused by a toxin. It is hypothesized that it results from lentinan (a polysaccharide found in the Shiitake mushroom) triggering blood vessels to dilate and leak small amounts of inflammatory compounds just beneath the skin. The rash typically neither hurts nor itches.
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