A case report of delayed positive reactions to photopatch tests with halogenated salicylanilides is presented. Because the reaction to the test may not appear for 96 hours, the skin sites should be observed longer than the usual 24 to 48 hours after photopatch testing.
Ison AE, Tucker JB. Delayed Reactions in Positive Photopatch Tests to Halogenated Salicylanilides. Arch Dermatol. 1967;96(1):59-61. doi:10.1001/archderm.1967.01610010065009