Delayed hypersensitivity to palladium dichloride: 15‐year retrospective study in a skin allergy unit

Background Metal allergies are the most frequent causes of allergic contact dermatitis. Although the use of palladium is increasing, it is not included in any baseline series. Objective To assess the prevalence of hypersensitivity to palladium and to describe the clinical and demographic characteristics of patients who are sensitized to palladium dichloride (PdCl2). Methods A single‐centre, retrospective study of 15 years of patch testing with the Spanish baseline series supplemented with PdCl2 2% pet. was performed. We collected clinical and demographic data and data on co‐sensitization among the metals studied, and we compared patients who were sensitized to palladium, with or without co‐sensitization to nickel, with the rest of the study population. Results Among the 3678 included patients, 730 (19.9%) were sensitized to nickel sulfate. The prevalence of sensitization to PdCl2 (n = 316, 8.6%) was higher than the prevalence of sensitization to potassium dichromate (n = 240, 6.5%) and similar to the prevalence of sensitization to cobalt chloride (n = 353, 9.6%). Only 26 (8.2%) of the patients sensitized to palladium were not co‐sensitized to nickel. The percentage of men and patients aged ≥40 years was higher in this subgroup than in the patients with nickel co‐sensitization. Conclusions Given the high prevalence of hypersensitivity to PdCl2, this metal salt should be included in the Spanish baseline series, notwithstanding the frequency of co‐sensitization to nickel.