Five patients with photoallergic contact dermatitis due to halogenated salicylanilides and chemically related antimicrobial agents are presented. Cross-photosensitivity is demonstrated between tetrachlorosalicylanilide, tribromosalicylanilide, and bithionol, but not with hexachlorophene. Ultraviolet light in the range of 3,200-4,500 Angstrom units is required for initiation of these photoallergic reactions. Histologically photoallergic contact dermatitis is identical with allergic contact dermatitis, but it is distinctly different from phototoxic contact dermatitis. Allergic contact sensitivity to some of these compounds may be present simultaneously with or without photoallergic contact sensitivity. The mechanism mediating photoallergic contact sensitivity to halogenated salicylanilides is proposed to be that light (3,600A) causes the formation of a free radical derivative which binds with cutaneous proteins. This new hapten-protein unit then acts as a photoantigen in a small percentage of the exposed population.
HARBER LC, HARRIS H, BAER RL. Photoallergic Contact Dermatitis: Due to Halogenated Salicylanilides and Related Compounds. Arch Dermatol. 1966;94(3):255–262. doi:10.1001/archderm.1966.01600270005001
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