Contact allergy to colophony : clinical and experimental studies with emphasis on clinical relevance

Abstract

Colophony - also called rosin - is a material obtained from coniferous trees. It is used widely in many products, particularly because of its good tackifying properties. Colophony is also used in paper sizing to increase water resistance. Colophony may cause contact allergy, and around 5% of Swedish dermatitis patients show allergic reactions to colophony at patch testing. There are many case reports of colophony in different products causing contact dermatitis. Often, however, the clinical relevance of a positive patch-test reaction to colophony is difficult to evaluate.

The principal aims of the present thesis were to study the prevalence of contact allergy to colophony and of skin disease in individuals with an occupational exposure to colophony; to study the prognosis of dermatitis in colophony-sensitive subjects, and to investigate the outcome of repeated open applications of colophony, thereby trying to elucidate the clinical relevance of contact allergy to colophony.

Employees of a tall-oil rosin (colophony) factory (n=180), and of an opera company where colophony was used in dancers' rosin, mascara and wig glues (n=132), were interviewed, examined and patch tested. 3.9% and 2% of these two groups respectively had a positive patch test to colophony. More than every fourth participant showed some kind of skin disease, but only few cases were related to work.

Eighty-three patients with previously diagnosed contact allergy to colophony were followed up. 72% showed a positive patch-test reaction to colophony at re-testing. Around one third had hand eczema. There was no significant correlation between colophony exposure and current hand eczema. Adhesive bandages containing colophony and zinc oxide (ZnO), colophony and mixes of colophony and ZnO, were tested in 7 colophony-sensitive subjects to see whether addition of zinc oxide inhibited elicitation of allergic dermatitis to colophony, which has been proposed. No difference in reactivity between colophony and colophony/ZnO was seen at patch testing, and there were positive patch-test reactions to all colophony-containing bandages. Thus no inhibitory effect of ZnO was shown.

Repeated open application tests were performed with cobalt chloride and colophony in sensitized guinea pigs. The animals were also patch-tested. A dose-response correlation was found with both cobalt chloride and colophony. There was a concordance between patch-test reactions and reactions at repeated open application tests, the higher the concentration of the allergen at the open test the stronger the concordance.

In 13 colophony-sensitive subjects serial dilution patch tests with colophony were performed followed by repeated open application tests using colophony of different concentrations once daily for two weeks. Reactions were assessed visually, by laser Doppler flowmetry and by measurements of transepidermal water loss. Ten subjects reacted at open applications with colophony 20%. The strength of the reaction varied greatly. A correlation between the threshold concentration at patch testing and the outcome of the repeated open application tests was found and also a dose-response relationship. Nine healthy controls did not react to repeated open applications with colophony. The measurements of transepidermal water loss and blood flow was of no additional use to visual assessment when evaluating repeated open application test reactions with colophony.