urushiol

A toxic substance composed of catechol derivatives that is present in the sap of various plants of the family Anacardiaceae and especially the genus Toxicodendron, including poison ivy, poison sumac, and the lacquer tree, from which a durable lacquer is obtained.

An oil found in plants of the family Anacardiaceae, causing an allergic skin rash on contact; consists of a variable mixture of several organic compounds.