Main Outcome Measures: Systematic investigation of different causes of pompholyx: fungal intertrigo, hyperhidrosis, atopy, contact eczema, and internal reactions with systematic provocation tests to metals, balsam of Peru, and food allergen when suspected.Results: The present study found the following causes of pompholyx in the 120 patients: mycosis (10.0%); allergic contact pompholyx (67.5%), with cosmetic and hy-giene products as the main factor (31.7%), followed by metals (16.7%); and internal reactivation from drug, food, or haptenic (nickel) origin (6.7%). The remaining 15.0% of patients were classified as idiopathic patients, but all were atopic. (Percentages do not total 100 because of rounding.)Conclusions: Our data confirm the existence of reactional pompholyx to interdigital-plantar intertrigos and endogenous reactions to metals or other allergens, but they mainly point at the unexpected importance of a socalled contact pompholyx in which cosmetic and hygiene products play a preponderant role compared with metals. The great frequency of atopic conditions, even if idiopathic pompholyx is not inferred as an equivalent of atopy, should lead to further causative investigations before undertaking more expensive or extensive treatments of refractory pompholyx.