Suppression of UV-induced erythema by topical treatment with melatonin. Influence of the application time point

The UV-suppressive effect of topical melatonin was assessed at different application time points in a double-blind randomized clinical trial. The lower back of 20 healthy volunteers was treated with 0.6 mg/cm2 melatonin or vehicle either 15 min before or 1, 30 or 240 min after UV irradiation. The erythema was evaluated visually and measured by chromametry 24 h after irradiation. UV-absorbing effects of melatonin were measured at a concentration of 8 microg/ml with a spectrophotometer. Melatonin absorbs UV light at a wavelength of 225-275 nm which is clearly below the wavelength of UVA and UVB (290-390 nm). The visual score showed that application of melatonin 15 min before irradiation significantly suppressed erythema compared to treatment with vehicle alone (p < 0.001). Similar results were found by chromametry (p < 0.001). Treatment after irradiation showed no UV suppression. The erythema suppressive effect of melatonin might be explained by the radical-scavenging mechanism of quenching meanly hydroxyl radicals (.OH) which are known to be most present in sunburn reaction of the skin. The protective effect of the pre-irradiation treatment might be explained by penetration into the skin within 15 min and the presence in a local concentration at the irradiation time point.