Pigmentation effects of blue light irradiation on skin and how to protect against them.

Background Visible light, in particular blue light, has been identified as an additional contributor to cutaneous photoageing. However, clinical studies demonstrating the clear effect of blue light on photoageing are still scarce, and so far, most studies have focused on broad-spectrum visible light. Although there is evidence for increased skin pigmentation, the underlying mechanisms of photoageingin vivoare still unclear. Furthermore, there is still a need for active ingredients to significantly protect against blue light-induced hyperpigmentationin vivo. Our study had two aims: to detect visible changes in skin pigmentation following repeated irradiation of the skin with LED-based blue light and to reduce pigmentation using suitable active ingredients. Method We conducted a randomized, double-blind and placebo-controlled clinical study on 33 female volunteers with skin phototypes III and IV. We used a repetitive blue light (4 x 60 J cm(-2), 450 nm) irradiation protocol on the volunteers' inner forearms. Using hyperspectral imaging, we assessed chromophore status. In addition, we took chromameter measurements and photographs to assess visible hyperpigmentation. Results We measured significant changes in chromophore status (P < 0.001 vs baseline), that is of melanin, haemoglobin and oxygen saturation, immediately after blue light irradiation. In addition, we found visible skin colour changes which were expressed by a significant decrease in ITA degrees values (delta ITA degrees = -16.89,P < 0.001 vs baseline for the placebo group) and an increase ina* (deltaa* = +3.37,P < 0.001 vs baseline for the placebo group) 24 h post-irradiation. Hyperpigmentation and skin reddening were mitigated by both a formulation containing 3% of a microalgal product and a formulation containing 3% niacinamide. Conclusion Our study sets out an efficient and robust protocol for investigating both blue light-induced cutaneous alterations, such as changes in skin chromophores, and signs of photoageing, such as hyperpigmentation. Moreover, we have shown evidence that both an extract of the microalgaScenedesmus rubescensand niacinamide (vitamin B3) have the potential to protect against blue light-induced hyperpigmentation.