Visible Red Light Enhances Physiological Anagen Entry In Vivo And Has Direct And Indirect Stimulatory Effects In Vitro

The study investigated the effects of visible light on hair follicles, focusing on red light (630 nm) compared to green and blue light. In vivo experiments on mice showed that red light accelerated the transition from telogen to anagen phase faster than the other lights. In vitro, red light stimulated the proliferation of outer root sheath keratinocytes and dermal papilla cells by promoting cell cycle progression through extracellular signal-regulated kinase phosphorylation. Additionally, red light enhanced epithelial-mesenchymal interactions, with fibroblast growth factor 7 playing a key role. These findings suggested that red light could promote hair growth by both direct and indirect mechanisms.