Copper--a rare sensitizer

To determine the incidence of patch test reactions to copper, 2% copper sulphate was included in our routine patch test series. The allergic potential of copper sulphate was evaluated by the guinea pig maximization test method (GPMT). 13 of the 1190 eczema patients showed reactions (1.1%), but they were considered non-relevant. 3 series of GPMT demonstrated that copper sulphate was a grade I allergen. A critical review of the literature disclosed that several reports on cases of allergic contact dermatitis to copper must be regarded as uncertain or non-relevant. 4 cases were considered relevant and another 20 cases probably relevant. It is suggested that a test reaction to copper sulphate should be verified by a serial dilution test (SDT). Furthermore, the sensitivity of patients to other metals should be stated, so that one can be aware that false positive reactions from metal impurities, especially nickel, in the copper salt used for testing may occur.