Allergic Contact Dermatitis

By Dr Jonathan S. Crane

For 5 years, a 54-year-old woman had been bothered by an intermittent dermatitis on her left hand and wrist (A). The rash had remained constant during the past year. The patient, a hairdresser, usually wears gloves when she works. Moderate erythema and flaking were noted on her hands. Based on the clinical findings and the patient’s occupation, allergic contact dermatitis was strongly suspected. A thin layer rapid use epicutaneous (TRUE) test of 24 allergens revealed a significant positive reaction to p-phenylenediamine, a constituent of the permanent hair coloring preparation the patient uses in her salon (B); this substance is also found in dark-colored cosmetics, black rubber, ink, oil, grease, and gasoline. Dr Jonathan S. Crane, John D. Schoonmaker, PA-C, and Patricia B. Hood, PA-C, of Wilmington, NC, write that allergic contact dermatitis occurs after exposure—frequently multiple exposures—to an antigenic substance. This delayed hypersensitivity reaction most commonly occurs on the hands and face. Many persons are exposed to potential sensitizing agents in the workplace. A patient’s occupation often is a clue to possible allergens; as in this case, patch testing can identify the allergen and confirm the diagnosis. This patient’s dermatitis resolved after she applied a medium-potency topical corticosteroid for 2 weeks. She was advised to use a p-phenylenediamine–free hair dye on her clients and to avoid sunscreens with para-aminobenzoic acid (PABA) and preparations that contain benzocaine(; these agents can cause cross-reactions in some persons with p-phenylenediamine allergy.