Effects of topical petrolatum and salicylic acid upon skin photoreaction to UVA.

Various agents which can be used in combination can also interfere with phototherapy. In this study, the effects of topical petrolatum and 20% salicylic acid in petrolatum upon skin photoreaction to UVA were investigated, in an in vivo test. Minimal phototoxic dose (MPD) test was performed on 31 volunteers and the test was repeated with thin (0.1 cc/25 cm(2)) petrolatum, thick (0.3 cc/25 cm(2)) petrolatum, thin 20% salicylic acid in petrolatum, thick 20% salicylic acid in petrolatum and sunscreen. The effect of each agent on MPD was investigated. MPD was increased with thin and thick applications of all agents. Also, MPD was increased with 20% salicylic acid in petrolatum when compared with pure petrolatum, in the same thickness. The application of petrolatum and salicylic acid in petrolatum just before PUVA therapy is not recommended because of their blocking effects.