Suppression of UV-induced erythema by topical treatment with melatonin (N-acetyl-5-methoxytryptamine) - Influence of the application time point

Background: In a previous study, we reported a significant and dose-dependent suppression of UV-induced erythema in human skin by a topically applied melatonin preparation. Objective: The present double-blind randomized study was designed to examine the influence of the application time point of topical melatonin on this antierythema effect. Methods: Defined small areas on the lower back of 20 volunteers were treated with 0.6 mg/cm(2) melatonin dissolved in a nanocolloid gel carrier either 15 min before or 1, 30 or 240 min after UV irradiation with twice the individual minimal erythema dose delivered by a Multiport Solar UV Simulator (UVA and UVB. The erythemata induced were evaluated by visual scoring and chromametry 24 h after irradiation. Results: Treatment of the skin with melatonin 15 min before UV irradiation proved to almost completely suppress the development of an UV-induced erythema. In contrast, no significant protective effects of melatonin were observed when it was applied after UV irradiation. Conclusion: Topically applied melatonin has a clear-cut protective effect against UV-induced erythema. Free radical scavenging of UV-generated hydroxyl radicals and interference with the arachidonic acid metabolism are possible mechanisms of the melatonin action.