Patch testing with pure palladium metal in patients with sensitivity to palladium chloride.

During a 15-month period, 536 patients being investigated for suspected contact dermatitis were patch tested with the European standard series and palladium chloride 1% pet. 13 patients (2.4%) had a positive allergic response to palladium chloride and all 13 were also allergic to nickel. 12 of these 13 patients consented to further patch testing with discs of pure palladium metal foil, and none reacted. We have shown previously that palladium chloride patch test material contains traces of nickel, and propose an explanation for these results in terms of the additive effect of allergens when tested in combination.