photoallergic contact dermatitis, a papulovesicular, eczematous, or exudative skin reaction that occurs 24 to 48 hours after exposure to light in a previously sensitized person. The sensitizing substance concentrates in the skin and requires chemical alteration by light to become an active antigen. Among common photosensitizers are phenothiazines, hexachlorophene, oral hypoglycemic agents, and sulfanilamide. Prevention requires avoidance of the photosensitizer and of sunlight. Treatment is the same as that for any other inflammatory dermatitis.
