Allergenic agent in contact dermatitis from Holigarna ferruginea.

9 of 10 patients who developed dermatitis following contact with Holigarna ferruginea and 5 of 35 asymptomatic volunteers showed a positive patch test reaction to 2% W/V acetone extract of the plant's resinous exudate. 6 albino rats were sensitized following 3 weekly applications of the same extract. Laccol (3-heptadecadienyl catechol) was identified as the active principle in the exudate.