Patch testing with allergens from modified rosin (colophony) discloses additional cases of contact allergy.

Most rosin (colophony) used today is chemically modified. Will contact allergy to modified rosin be overlooked when testing is performed with only unmodified rosin in the standard series? 2 components from modified rosins, maleopimaric acid (MPA) and glyceryl I-monoabietate (GMA), earlier identified as contact allergens, were added to the patch test standard series. Some commonly-used modified rosin products were also tested. Positive reactions were observed to the modified components MPA and GMA. Of the patients with positive reactions to MPA and GMA, several did not react to unmodified rosin in the standard series. No reaction was observed to the modified rosin products without a concomitant reaction to unmodified rosin. The positive reactions observed to the modified rosins may be due to residual unmodified material in the product, but a possible contribution from allergenic modified rosin components cannot be disregarded. When a patient's history indicates a rosin allergy, but a negative response to unmodified rosin in the standard series is observed, additional testing with GMA and MPA or, second best, with glycerol-esterified rosin and maleic-anhydride-modified rosin is recommended. Some modified rosin products, which could be used for additional testing, are suggested.