Enhancement of hair follicle regeneration by non-ablative fractional laser: assessment of irradiation parameters and tissue response

Wu YF, Wang SH, Wu PS, Fan SM, Chiu HY, Tsai TH, Lin SJ.

Lasers Surg Med. 2015 Apr;47(4):331-41. doi: 10.1002/lsm.22330.

Non-ablative laser treatment is a new approach to hair loss. In this paper, Wu et al. assessed the effect of a 1550 nm erbium laser on the transition of telogen hairs to anagen in mice. The authors shaved 8-week-old mice whose hair follicles were in telogen and treated the skin once with the laser up to minor thermal injury. They found that irradiation at a density of 1048 MTZ/cm2 and an energy of 15 mJ could trigger a premature transition to anagen. One to three days after treatment, inflammation was seen around the follicles, which later resolved. By day 5, the authors observed proliferation of hair germ cells, followed 2 days later by proliferation of bulge stem cells. One theory of hair growth in mice after hair removal holds that injury and apoptosis of hair germ cells may activate stem cells in the bulge. Minor thermal injury to the skin may have a similar effect and bring about a premature return to anagen, as with the non-ablative laser in this study.