Application of topical petrolatum and salicylic acid blocks UVB and reduces MED

Journal of Drugs in Dermatology, August, 2003

This single-blind, vehicle-controlled study aimed to determine the effect of topical petrolatum and salicylic acid on the minimal erythema dose (MED). Thirty-five subjects underwent phototesting to determine their MED for UVB. In addition, four additional parallel rows of skin were tested with varying doses of UVB, after application of different topical agents. The second, third, fourth, and fifth rows consisted of a thin (.1 cc / 25 [cm.sup.2]) layer of white petrolatum, a thick (.3 cc / 25 [cm.sup.2]) layer of white petrolatum, a thin (.1 cc / 25 [cm.sup.2]) layer of salicylic acid, and a thick (.3 cc / 25 [cm.sup.2]) layer of salicylic acid, respectively. Each row was irradiated with UVB at increments of 20 mJ / [cm.sup.2] immediately after the application of the agents.

The findings showed that MED values were increased by a thin or thick application of petrolatum and also by a thin or thick application of salicylic acid (20%) in petrolatum. The highest MED values were detected with thick salicylic acid, followed by thin salicylic acid, thick petrolatum, and then thin petrolatum. These findings suggest that topical agents commonly used for psoriatic patients should not be used prior to UVB treatments.

Fetil E et al. Effects of topical petrolatum and salicylic acid on the erythemogenicity of UVB. Eur J Dermatol 2002; 12:154-56.