Contact allergy due to colophony (III). Sensitizing potency of resin acids and some related products.

7 resin acids, 3 synthetically prepared derivatives and the neutral fraction of Chinese colophony were studied by experimental sensitization using a modified FCA method. 4 resin acids, laevopimaric, abietic, podocarpic and tetrahydroabietic, proved to be weak sensitizers. Neoabietic, dehydroabietic, isopimaric acid and larixol remained negative. However, the derivatives, methyl abietate and calcium abietate, were shown to be moderate sensitizers, and the maleic-modified adduct to be a moderate to strong sensitizer. As laevopimaric acid plays only a minor rôle in colophony, abietic acid must be considered a major, even if weak, allergen in non-modified colophony. The neutral fraction of colophony is also partially involved in colophony allergy.