Urushiol is any of several chemicals found in plants of the family Anacardiaceae, especially Toxicodendron, such as poison ivy, and causing the rash on contact. It is named for urushi, a lacquer produced by Japanese from the sap of Toxicodendron trees called kiurushi. Chemically it is 1-alkyl phene-2,3-ol; the alkyl group has 15 or 17 carbons and may be unsaturated, depending on species.
