Oak moss extracts in the diagnosis of fragrance contact allergy

Oak moss absolute is one of the eight ingredients of the fragrance mix (FM) used for diagnosing perfume allergy. Oak moss absolute is an extract prepared from the lichen Evernia prunastri growing on oak trees. It has been shown that the oak moss patch test material from one producer contained resin acids which are ingredients of another lichen, tree moss. Resin acids, e.g. abietic acid and dehydroabietic acid, are also the main allergens in colophonium. The aim of the study was to assess whether the contamination of oak moss absolute and thus the FM with resin acids had affected their diagnostic value so that they, instead of indicating fragrance allergy, had become indicators of allergy to resin acids and thus colophonium. Two studies were undertaken. First the relationship between patch test reactions to FM, oak moss absolute, both with contents of resin acids, and colophonium were assessed in 885 consecutive patients. A significant relationship between reactions to colophonium and FM was seen (p < 0.001) as well as a significant relationship between oak moss absolute and colophonium (p < 0.001). The relationship between colophonium and FM was still significant when all reactions to oak moss absolute were disregarded (p < 0.001), showing a relationship also between colophonium and fragrance ingredients other than oak moss absolute. Second, 119 consecutive patients were tested with an old and a new version of oak moss absolute containing resin acid (0.05%) and no measurable resin acid, respectively, and with the corresponding FM. No overall difference in reactivity to the old and new version of oak moss absolute/FM was seen. It is concluded the diagnostic value of oak moss absolute as indicator fragrance contact allergy has been and is unaffected by the resin acid contamination.