It has long been known that red or near-infrared laser light promotes tissue repair and regeneration and low-intensity light called low-level laser therapy (LLLT) stimulates cellular activity [1]. After the discovery of lasers in the 1960s, there has been tremendous interest in using these laser devices to treat various medical conditions. The most commonly used devices have wavelengths in the range 500–1,100 nm (the so-called optical window of tissue) and they deliver fluences of 1–10 J/cm2 with a power density of 3–90 mW/cm2. LLLT has shown beneficial effects for a variety of medical conditions such as wound healing, nerve regeneration, joint pain relief, stroke recovery, and the prevention and treatment of mucositis [2–8]. Home-use LLLT devices that emit low power coherent monochromatic red light have been developed for various skin conditions, including hair growth [9]. In this review, we will focus on the use of LLLT as a potential treatment for several types of hair loss.

Alopecia is a common disorder affecting more than half of the population worldwide. Androgenetic alopecia, the most common type, affects 50% of males over the age of 40 and 75% of females over 65. Only two drugs have been approved so far (minoxidil and finasteride) and hair transplant is the other treatment alternative. This review surveys the evidence for low-level laser therapy (LLLT) applied to the scalp as a treatment for hair loss and discusses possible mechanisms of actions.

Studies have shown that LLLT stimulated hair growth in mice subjected to chemotherapy-induced alopecia and also in alopecia areata. Controlled clinical trials demonstrated that LLLT stimulated hair growth in both men and women. Among various mechanisms, the main mechanism is hypothesized to be stimulation of epidermal stem cells in the hair follicle bulge and shifting the follicles into anagen phase.