Visible Light-Induced Pigmentation: Improved In Vivo Methodology for Measuring Efficacy of 30 Products in 9 Randomised Controlled Trials and Correlation With In Vitro Assessment.

As hyperpigmentation can worsen with exposure to ultraviolet (UV) and visible light (VL), sunscreens with well-balanced UVB/UVA protection and VL-blocking pigments are recommended. Assessing efficiency against VL-induced pigmentation is then mandatory. Recently, an in vivo pigmentation assessment allowing a VL protection factor (pVL-PF) determination, and an in vitro predictive method based on transmittance measures were introduced. However, the number of volunteers, tested sunscreens, and protection range were limited. Moreover, no statistical assessment was associated. This study aimed at testing the robustness and improving these methodologies by conducting a series of 9 monocentric, double-blind, randomised controlled in vivo studies involving 188 volunteers and 30 products, alongside an in vitro approach, in 2 independent laboratories. Our results first allowed us to improve pVL-PF calculation by better fitting to VL-induced pigmentation dynamics. Based on the 30 established pVL-PF, we evidenced that VL-protection level strongly correlated with the amount of pigments in products. Second, a statistical Bayesian approach, accounting for kinetic and inter-individual response variability over time, was proposed. This enabled us to determine that 24 out of 30 products significantly reduced VL-induced pigmentation. Finally, we showed that in vitro transmittance reduction was highly predictive of in vivo results. In conclusion, through several independent studies involving a large number of products and volunteers, a refined pVL-PF calculation associated with statistical indicators was proposed together with a predictive in vitro assessment. These methodologies to assess the efficacy of tinted products against VL-induced pigmentation are complementary and could also be of interest for other pathologies induced or aggravated by VL. Trial Registration: NCT06827392, NCT06796192, NCT06803901, NCT06796140, NCT06796153, NCT06796010, NCT06796088, NCT06796205, NCT06796179.