High-intensity flashlamp photoepilation: a clinical, histological, and mechanistic study in human skin.

OBJECTIVE To examine the clinical, histological, and immunohistological effects of flashlamp photoepilation. DESIGN Nonrandomized control trial with blinded histological study and follow-up of 1 to 20 months. SETTING Private academic practice. SUBJECTS Sixty-seven subjects (10 males and 57 females) with areas of excess body hair. INTERVENTIONS Single (9 subjects) or multiple (58 subjects) treatments (noncoherent, 590-1200 nm, 2.9-3.0 milliseconds, 40-42 J/cm2) to hairy skin. From subjects given a single treatment, biopsy samples were taken immediately after treatment and at different intervals for up to 20 months. MEAN OUTCOME MEASURES Clinical measures include hair counts and morphologic features before and after treatment. Histological measures include terminal-vellus and anagen-other ratios, hair shaft diameter, and morphologic features (routine and immunohistochemical detection of bcl-2, bax, p53, Ki67, cyclin D1, and hsp70) before and after treatment. RESULTS Mean hair loss after photoepilation was 49%, 57%, and 54% for a single treatment and 47%, 56%, and 64% for multiple treatments at follow-up of less than 3 months, 3 to less than 6 months, and 6 months or longer, respectively (P<.05 for all comparisons). Transient erythema was seen in all subjects; no scarring occurred. Histologically, treatment caused morphologic damage confined to hair follicles and shafts. Terminal-vellus and anagen-telogen ratios, mean hair shaft diameter, and immunohistochemical profiles were not significantly modified by treatment. Treatment did not alter other skin adnexa, epidermis, or vessels. CONCLUSIONS Flashlamp treatment leads to significant, longlasting epilation. The predominant mechanism seems to be via selective photothermal damage to large, pigmented hair follicles rather than induction of a programmed state of follicular cycle arrest or follicular miniaturization.