Hair loss can cause psychological distress. Here, red organic light-emitting diode (OLED) light source is first introduced as the photobiomodulation therapy (PBMT) for hair growth and demonstrated as a promising and non-invasive therapeutic modality for alopecia. OLED exhibits unique advantages of homogeneous irradiation, flexible in form factor, and less heat generation. These features enable OLED to be an ideal candidate for wearable PBMT light sources. A systematic study of using red OLEDs to facilitate hair growth was conducted. The results show that OLEDs excellently promote hair regrowth. OLED irradiation can increase the length of the hair by a factor of 1.5 as compared to the control, and the hair regrowth area is enlarged by over 3 times after 20 days of treatments. Moreover, the mechanism of OLED that stimulates hair follicle regeneration is investigated in-vivo by conducting a systematic controlled experiments on mice with or without OLED PBMT. Based on the comprehensive histological and immunofluorescence staining studies, two key factors are identified for red OLEDs to facilitate hair follicle regeneration: (i) increased autophagy during the anagen phase of the hair growth cycle; (ii) increased blood oxygen content promoted by the accelerated microvascular blood flow.