A precise analysis of the relative contribution of UVA1 and visible light colour domains in solar light‐induced skin pigmentation

Abstract Background Solar light induces or aggravates hyperpigmentation issues. The contribution of UVA1, as well as visible light (VL), especially high‐energy blue‐violet visible (HEV) light, is now clearly established. Objectives This work aimed at determining the relative contribution of UVA1, HEV and VL wavelength bands and their sub‐domains in pigmentation induction. Methods Two clinical studies using solar simulators equipped with specific bandpass physical filters were carried out. Volunteers (FSPT III‐IV) were exposed on the back to UVA1 + HEV (350–450 nm), UVA1 (350–400 nm), HEV (400–450 nm) or part of UVA1 + HEV (370–450 nm) in Study 1 ( n = 27) and to VL (400–700 nm), HEV (400–450 nm), Blue (400–500 nm), Green (500–600 nm) and Green+Red (500–700 nm) domains in Study 2 ( n = 25). Pigmentation level was assessed by visual scoring and colorimetry at different time points postexposure, up to Day 43. Results Induced pigmentation was detected in all exposed conditions, peaking at 2 h and thereafter progressively decreasing but remaining persistent up to Day 43. In Study 1, UVA1 showed an additive effect with HEV, with a significant contribution coming from the Longest UVA1 rays (370–400 nm). Study 2 demonstrated that 24 h postexposure, the Blue domain accounted for 71% of VL‐induced pigmentation, the HEV one for 47%, the Green one for 37% and the Green+Red one for 36%, confirming no significant effect for Red light. Conclusions Altogether, these results underline the need for UVA1 photoprotection up to 400 nm and highlight the importance of protecting the skin from solar VL wavelengths and especially from HEV, Blue and Green light, to limit induced pigmentation.