A method to assess the protective efficacy of sunscreens against visible light-induced pigmentation

Until now, photoprotection of human skin has involved the development of sunscreens effective in the ultraviolet (UV) domain. During the last ten years, several studies have shown that besides the well-known damaging effects of UV, visible (400-700 nm) and even infrared light (> 700 nm) can induce damage which contributes to photoaging. Furthermore, many photodermatoses are also known to be triggered by visible light (VL).

An in vivo method is proposed to assess the protective efficacy of sunscreens in the VL domain. This method is based on the intensity of pigmentation induced by four repeated daily doses of VL, each equivalent to about one hour of midday sun. Exposures are performed using a solar simulator (xenon lamp) equipped with appropriate filters, and pigmentation is measured both clinically and by chromametry. Three commercially available sunscreens designed to protect in the visible range were evaluated.

The results indicate that the VL-induced pigmentation was already significantly detectable visually and by chromametry 24 hours after the first exposure on the unprotected zone. Two products with moderate protective activity could be differentiated from the untreated zone from Day 3 to Day 5 and were also significantly less effective than a third tested product within the same study period.

The method is simple, based on a clinical end point of VL-induced skin pigmentation, and can be performed within a 5-day period. It allows discrimination between products of different protective capacities. VL protection factor is also discussed.