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 photo-aging. However, clinical studies demonstrating the clear effect of blue light on photo-aging are still scarce and so far, most studies have focused on broad spectrum visible light. While there is evidence for increased skin pigmentation, the underlying mechanisms of photo-aging in vivo are still unclear. Furthermore, there is still a need for active ingredients to significantly protect against blue light induced hyperpigmentation in 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 (4x 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), i.e. of melanin, hemoglobin and oxygen saturation, immediately after blue light irradiation. In addition, we found visible skin color changes which were expressed by a significant decrease in ITA° values (delta ITA° = -16.89, p<0.001 vs baseline for the placebo group), and an increase in a* (delta a* = +3.37, p<0.001 vs baseline for the placebo group) 24 hours 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 photoaging, such as hyperpigmentation. Moreover, we have shown evidence that both an extract of the microalga Scenedesmus rubescens and niacinamide (Vitamin B3) have the potential to protect against blue light induced hyperpigmentation.