Effects of photobiomodulation at various irradiances on normal and dihydrotestosterone‐treated human hair dermal papilla cells in vitro

Androgenetic alopecia (AGA) is the most common type of hair loss caused by dihydrotestosterone (DHT) binding to androgen receptors in dermal papilla cells (DPCs). Photobiomodulation (PBM) is a promising treatment for AGA but suffers from inconsistent outcomes and inconsistent effective light parameters. This study investigated the impact of red light at various irradiances on normal and DHT‐treated DPCs. Our results suggested that red light at 8 mW/cm2 was most effective in promoting DPCs growth. Furthermore, a range of irradiances from 2 to 64 mW/cm2 modulated key signaling pathways, including Wnt, FGF, and TGF, in normal and DHT‐treated DPCs. Interestingly, 8 mW/cm2 had a greater impact on these pathways in DHT‐treated DPCs and altered the Shh pathway, suggesting that the effect of PBM varies with the cellular environment. This study highlights specific factors that influence PBM effectiveness and provides insight into the need for personalized PBM treatment approaches. Red light at an irradiance of 8 mW/cm2 effectively promoted the growth of normal and DHT‐treated DPCs in vitro. It modulated key signaling pathways, including Wnt, FGF, and TGF, and also affected the Shh pathway in DHT‐treated DPCs.