Visible light between 400 to 500nm was identified as an additional contributor to cutaneous photo-aging. Clinical studies showing clear effects of blue light on photo-aging are, however, still scarce. While there is evidence for increased skin pigmentation, the underlying mechanisms of photo-aging in vivo are still not clear. Furthermore, there is still a lack of means to significantly protect from blue light induced signs of photo-aging in vivo.
We conducted a randomized, double-blind and placebo controlled clinical study on 33 female Caucasian and Asian volunteers with skin phototype III and IV. We used a repetitive (4x 60J/cm2, 450 nm) irradiation protocol to induce visible skin pigmentation on inner forearms. We did chromameter measurements to assess skin pigmentation. Using hyperspectral imaging we assessed chromophore status. In addition, we took tape strips which we analyzed for carbonylated proteins.
We found significant pigment darkening due to repetitive blue light irradiation (delta ITA° = -16.89, p<0.001 vs baseline for the placebo group). Chromophore status showed an increase in melanin after day 4 and temporary increase in hemoglobin and blood oxygen saturation after blue light irradiation. In addition, protein carbonylation increased. Concerning mitigation of the visible signs of blue light induced cutaneous changes, we found that volunteers using a microalgae extract experienced a significantly lower pigment darkening effect compared to the placebo group (delta ITA° = - 11.27, p<0.05 vs placebo).
We show an efficient and robust protocol to investigate blue light induced cutaneous changes like pigment darkening and signs of photoaging, like protein carbonyls. Furthermore, we propose an extract of the microalga Scenedesmus rubescens as an efficient means to protect from visible, blue light induced photoaging.

Blue light induced cutaneous signs of photo-aging and protection of the visible effects