A new in vitro method to predict in vivo photoprotection of skin hyperpigmentation induced by visible light

Abstract

Background: Ultraviolet radiation is the main cause of skin pigmentation, but more recently visible light has been shown to be an important contributor especially in melano-competent subjects. Photoprotection from visible light can improve several hyperpigmentation disorders. Recently, a visible light photoprotection assessment method has been proposed based on in vivo pigmentation; the visible light photoprotection factor (VL-PF) is determined by assessment of the change in colorimetry parameter ITA over several days measured using a chromameter. Although in vivo methods remain the most representative of real life, in vitro methods are more suited to screening sunscreen formulations.

Objective: The aim of this study was to evaluate the correlation between in vivo and in vitro methods in assessing protection against visible light induced pigmentation.

Methods: We first analysed the in vitro protective properties of the 10 commercially available sunscreens using transmission measurements in the visible spectrum. Then, we performed a monocentric, double-blind, randomized controlled study with intra-individual comparisons in 20 healthy subjects and measure the VL-PF in vivo of those sunscreens. The correlation between the VL-PF and the percentage of blocked light was evaluated using the coefficient of determination R² .

Results: A strong significant correlation was demonstrated between in vivo visible light protection factor and in vitro transmittance measurements, with the highest correlation factor at 420 nm and in the spectrum covering from 400 to 469 nm.

Conclusion: Transmittance measurements were found to be a good predictive tool to evaluate sunscreen visible light photoprotection efficacy and could be used to select formulations for final in vivo testing.

Figure 1

Transmission spectra of the 10 tested sunscreens (A to J).

Figure 2

In vivo evaluation of the protection against VL‐induced pigmentation of 10 tested sunscreens (A to J). (a) The visible protection was calculated with the VL‐PF and (b) the pVL‐PF=(1‐(1/VL‐PF))×100. Bold dashed line corresponds to the minimum protection and the light dashed line to the maximum protection. (c) Eleven photos showing on the right side the exposed areas and on the left side unexposed areas, all of which were previously treated with sunscreen as indicated in Figure 2.

Figure 3

Correlation between the in vivo protection against VL‐induced pigmentation and the amount of VL blocked in vitro by the 10 tested sunscreens. Correlations at 420 nm (a) and between 400 and 469 nm (b).