Temporary hair removal by low fluence photoepilation: histological study on biopsies and cultured human hair follicles.

BACKGROUND AND OBJECTIVES We have recently shown that repeated low fluence photoepilation (LFP) with intense pulsed light (IPL) leads to effective hair removal, which is fully reversible. Contrary to permanent hair removal treatments, LFP does not induce severe damage to the hair follicle. The purpose of the current study is to investigate the impact of LFP on the structure and the physiology of the hair follicle. STUDY DESIGN/MATERIALS AND METHODS Single pulses of IPL with a fluence of 9 J/cm(2) and duration of 15 milliseconds were applied to one lower leg of 12 female subjects, followed by taking a single biopsy per person, either immediately, or after 3 or 7 days. Additionally, we present a novel approach to examine the effects of LFP, in which ex vivo hairy human scalp skin was exposed to IPL pulses with the same parameters as above, followed by isolation and culturing of the hair follicles over several days. Samples were examined histologically and morphologically. RESULTS The majority of the cultured follicles that had been exposed to LFP treatment showed a marked treatment effect. The melanin containing part of the hair follicle bulb was the target and a catagen-like transformation was observed demonstrating that hair formation had ceased. The other follicles that had been exposed to LFP showed a less strong or no response. The skin biopsies also revealed that the melanin-rich region of the hair follicle bulb matrix was targeted; other parts of the follicle and the skin remained unaffected. Catagen/telogen hair follicles were visible with unusual melanin clumping, indicating this cycle phase was induced by the IPL treatment. CONCLUSIONS Low fluence photoepilation targets the pigmented matrix area of the anagen hair follicle bulb, causing a highly localized but mild trauma that interrupts the hair cycle, induces a catagen-like state and eventually leads to temporary loss of the hair.