Bithionol is a primary photosensitizer.
Cross-reactions occurred with tetrachlorosalicylanilide (TCSA), tribromosalicylanilide (TBS), and hexachlorophene but not with trichlorocarbanilide (TCC).
Photopatch tests produced relatively characteristic responses for each substance.
Reactions to TBS and TCSA in patients with contact photodermatitis from bithionol represent true photo-cross-sensitivity.
Reactions to hexachlorophene in these patients with contact photodermatitis from bithionol did not require light. These reactions represent the unusual phenomenon of crosssensitivity between a photosensitizer and a simple contact allergen.
BAUGHMAN RD. Contact Photodermatitis From Bithionol: II. Cross-Sensitivities to Hexachlorophene and Salicylanilides. Arch Dermatol. 1964;90(2):153–157. doi:10.1001/archderm.1964.01600020021003
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