Clinical experience and patch testing using colophony (rosin) from different sources.

Patients with suspected allergy to colophony were patch-tested with colophony (rosin) of different kinds (gum rosin, tall oil rosin). More cases of allergy were detected by testing with more than one type of colophony. Tall oil rosin produced a smaller number of positive reactions than the gum rosins tested, which suggests a lower allergenic activity. Venice turpentine was a useful additional screening substance. When different test concentrations were compared (20% and 5%) the lower concentration failed to reveal four of 30 cases. The patients' eczema had been caused chiefly by contact with colophony in their work.