- The toxic irritant principle of poison ivy and related plants.
- Urushiol is an oily mixture of organic compounds with allergenic properties found in plants of the family Anacardiaceae, especially Toxicodendron spp. (e.g., poison oak, Chinese lacquer tree, poison ivy, poison sumac) and also in parts of the mango tree.
- 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.