Identification of contact allergens in unmodified rosin using a combination of patch testing and analytical chemistry techniques.

In order to investigate the contact allergens in the unmodified colophony (rosin) used in routine patch testing, preparative chromatographic techniques were used to separate its components which were then patch tested on colophony-sensitive individuals. The chemical structure of the dermatologically active components was elucidated using mass spectrometry, nuclear magnetic resonance and infra-red techniques. The study shows that oxidized resin acids are stronger sensitizers than the resin acids themselves, the most potent contact allergen being 7-oxydehydroabietic acid (purity 92%). At naturally occurring concentrations (relative to abietic acid) all unoxidized resin acids were found to play an insignificant part, individually, in colophony dermatitis, except abietic acid (purity 99%), which was found to be a weak but important allergen. The commercial Trolab abietic acid preparation (unknown purity) was found to be dermatologically more active than purified abietic acid.