Arnica montana L. (plant family: Compositae) is one of the oldest and most important drug plants. Besides its healing effects it also reveals sensitizing properties. From the literature more than 35 references with more than 100 cases of contact dermatitis could be cited, completed by four own cases. In most cases sensitization was induced by self treatment with tincture of Arnica, whereas occupational contact dermatitis in drug sellers of pharmacists is rare. Chemical and animal experimental investigations corroborated the high sensitizing capacity of Arnica montana L. and near related Arnica species. The low toxic threshold often causes also primary toxic skin reactions. The sesquiterpene lactones helenalin, its acetate and methacrylate have been proved to be the primary sensitizers. As more Arnica-containing drugs are entering the market it is proposed to include Arnica again in the standard test series.
