Assessment by mouse model of the ultraviolet A protective effect of topical sunscreens

We have developed an animal model to assess the ultraviolet A (UVA) protective effect of topical sunscreens with the use of BALB/cJ mice in which contact photosensitivity to 3, 3', 4', 5 tetrachlorosalicylanilide had been induced. The mice were sensitized on the clipped dorsal skin and challenged on the ears. Changes in ear thickness after challenge were used to measure the degree of photosensitivity. The efficacy of two doses of each topical sunscreen was assessed by the degree of suppression of the contact photosensitivity response at challenge. Control studies were performed with the base of each sunscreen. Some but not all sunscreens that contained UVA-absorbing chemicals showed active suppression of contact photosensitivity in this test system. Several sunscreens gave greater suppression at 5 microliters/cm2 than at 2 microliters/cm2, which suggests a dose-related effect. One sunscreen, however, gave greater suppression at 2 microliters/cm2. Several of the bases tested also suppressed the contact photosensitivity response. An unexpected finding was an enhancement of the contact photosensitivity reaction by two of the bases tested.