Urushiol is the allergenic agent found in most parts of the plant. Damage to plant tissues causes the nonvolatile chemicals to be exposed. Humans are often sensitized, with symptoms ranging from mild itchiness and redness to severe oozing lesions with fever. Poison ivy is probably responsible for more cases of plant dermatitis in Canada than any other plant. Urushiol can contaminate clothes, tools, and the fur of domestic animals.
Humans can subsequently develop dermatitis from contact.
Urushiol, a group of alkylcatechols, is found in the sap of poison-ivy plants. The allergic reaction has been traditionally thought to involve initial oxidation by which a protein-reactive quinone is formed. Recent work indicates that redox cycling in the skin, following penetration of the allergenic alkybenzenes, initially depletes local levels of endogenous-reducing equivalents such as NADH and glutathione. Further cycling results in the uncontrolled generation of radical species that exhibit protein reactivity. The urushiol is not volatile and can contaminate clothing, tools, and domestic animals.