Contaminating resin acids have not caused the high rate of sensitivity to oak moss

Commercially available oak moss absolute patch test material has recently been shown to contain resin acids of the type found in colophony (colophonium). We wished to assess whether the high frequency of positive patch tests to oak moss absolute at this institute was likely to reflect significant contamination by resin acids. The rate of positive reactions to colophony among our oak moss-allergic patients patch tested during 1984-2000 was retrospectively investigated. 25395 patients were tested to the European standard series during this period and 1963 (7.7%) were allergic to the fragrance mix. 342 of these patients were allergic to oak moss absolute, of whom 73 (21.3%) were allergic to colophony. In comparison, 115 (13.4%) of 861 fragrance mix-positive but oak moss-negative patients were allergic to colophony (p = 0.0002, Fisher's exact test). This strongly statistically significant association between oak moss absolute and colophony shows only a small increase in rates of allergy to colophony in oak moss-positive patients. Thus we conclude that contaminating resin acids have not alone caused the high rate of sensitivity to oak moss.