Spa contact dermatitis.

Potassium monopersulfate (MPS) is widely used in spa and pool "shock" treatments, yet contact dermatitis associated with MPS has been rarely reported. A patient presented with a generalized scattered dermatitis from the neck down that worsened after spa use. Patch testing elicited a ++ reaction to ammonium persulfate. Contact with ammonium persulfate was ruled out; however, MPS, which can cross-react with ammonium persulfate, was found to be the active ingredient in the patient's spa shock treatments. The dermatitis cleared after the patient switched to a hydrogen peroxide-based shock treatment.