UVB erythema inhibited by topically applied substances.

The photoprotective and antierythematous effects of topical corticosteroids, acetylsalicylic acid (ASA), indomethacin (IM), butylhydroxytoluene (BHT) and diphenhydramine hydrochloride (DPH) and the influence of the application time on the formation of erythema were studied in healthy volunteers. The test substances, incorporated in o/w creams, were applied to the back in large Finn Chambers 24, 4 and 1 hours before and 1 and 4 hours after ultraviolet light B (UVB) irradiation (3 x MED). The reactions were assessed both visually and using a laser Doppler flowmetry device. When applied before irradiation, ASA and IM, significantly inhibited UVB erythema. When applied after irradiation, IM, DPH and potent corticosteroids reduced UVB erythema, but ASA, BHT and hydrocortisone did not. 5% ASA had the greatest photoprotective effect when the cream was applied 4 hours or 1 hour before irradiation. The photoprotective effect was only slight when the 5% ASA cream was applied 24 hours before irradiation.