Effect of red light on epidermal proliferation and mitochondrial activity

We previously demonstrated that irradiation with red light accelerates recovery of the epidermal water-impermeable barrier, whereas blue light delays it, and white and green light have no effect. Here, we aimed to examine in detail the effects of red and blue light in a human epidermal-equivalent model and in human skin. We used light-emitting diodes (red light, 630 nm, 6.2 mW/cm ; blue light, 463 nm, 6.2 mW/cm ) for irradiation of an epidermal-equivalent model and human skin. Cell proliferation was evaluated by means of BrdU and Ki-67 staining, and mitochondrial activity was quantified with an extracellular flux analyzer. Irradiation of the epidermal-equivalent model with red light for 2 h (44.64 J/cm ) increased both epidermal proliferation in the basal layer and mitochondrial activity. Blue light had no effect on epidermal proliferation. Furthermore, irradiation with red light for 2 h on three consecutive days increased epidermal proliferation in human skin tissue in culture. These results suggest that red light accelerates epidermal proliferation in both an epidermal-equivalent model and human skin, and may promote epidermal homeostasis.