Urushiol

Urushiol is the oily, catechol-based main component of urushi lacquer sap (roughly 60–70% of raw lacquer) and the substance responsible for forming the lacquer film: in the presence of oxygen and moisture, the laccase enzyme polymerizes urushiol into urushi’s hard, durable, glossy coating. Before it cures, urushiol is also a potent contact allergen that can cause an itchy skin rash (allergic contact dermatitis); once fully hardened, the lacquer is inert.