Contact allergy to colophony. Chemical identifications of allergens, sensitization experiments and clinical experiences.

Colophony (rosin) is a widespread material which is obtained from species of the family Pinaceae. It has a complex chemical composition, which differs depending mainly on the recovery process. The global production is about one million tons a year and the largest single consumption is in the sizing of paper and paper board. Rosin is a common cause of contact allergy and is included in the standard tray for patch testing at dermatological clinics. Unmodified gum rosin is the material mainly used in the routine series. It is desirable to test with identified allergens in order to make the testing and diagnosis more reliable and establish a strategy for prevention. The principal aims of the present study were to compare the allergenicity of rosin of different origins, to isolate and identify some of the allergens in unmodified gum rosin, and to attempt to diminish the allergenic potential of rosin preparations. Tall oil rosin and different types of gum rosin were tested in guinea pigs and in man. The test reactivity corresponded well when comparing gum rosin from different sources, while tall oil rosin showed a lower reactivity. However, testing with more than one rosin preparation in the routine series detected additional cases. A clear dose-response relationship was obtained by patch testing with gum rosin, implying that a concentration of 10% in petrolatum is well worth considering for routine testing. Unmodified Portuguese gum rosin was fractionated by chromatographic methods. Isolated fractions and components were tested for eliciting activity in guinea pigs sensitive to gum rosin. Pure compounds were also tested in patients with known allergy to gum rosin. The structures of the isolated allergens were elucidated using spectroscopic methods. Abietic acid, the classical colophony allergen, was found not to be allergenic, while oxidation products of abietic acid and dehydroabietic acid were identified as allergens. The isolated allergens showed a pattern of cross-reactivity in the animal experiments as well as among patients with known allergy to gum rosin. 15-Hydroperoxyabietic acid was identified as one of the main allergens, apparently formed by air oxidation of abietic acid. Gum rosin was hydrogenated in order to minimize the content of easily oxidized acids of the abietic type. The hydrogenated gum rosin showed a reduced allergenic activity compared to unmodified rosin both in animal experiments and patch testing in man.