Effect of red light on epidermal proliferation and mitochondrial activity

BACKGROUND/PURPOSE: 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. METHODS: We used light‐emitting diodes (red light, 630 nm, 6.2 mW/cm(2); blue light, 463 nm, 6.2 mW/cm(2)) 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. RESULTS: Irradiation of the epidermal‐equivalent model with red light for 2 h (44.64 J/cm(2)) 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. CONCLUSION: These results suggest that red light accelerates epidermal proliferation in both an epidermal‐equivalent model and human skin, and may promote epidermal homeostasis.