Allergic potential of neutrals in unmodified colophony, and a method for their separation from resin acids.

An ion-exchange fractionation technique for the separation of total resin acid and neutral fractions of unmodified colophony is described. The allergic potential of these fractions was assessed by patch testing colophony-sensitive individuals, and this showed that both the neutral components and the resin acids play an important role in colophony sensitization. A greater frequency of positive reactions was obtained using the 60% colophony patch test preparation compared with the currently recommended 20% colophony preparation. Furthermore, some individuals were found to produce positive reactions to only the neutral components in colophony. We suggest that the use of a colophony patch test battery comprising resin acids, neutrals, oxidized resin acid and some colophony derivatives, will facilitate detection of colophony-sensitive individuals. Moreover, we consider that this will help to provide a better estimate of the prevalence of colophony dermatitis, which is currently underestimated.