INTRODUCTION/OBJECTIVE : This study aimed to evaluate the safety and efficacy of a 3.5 ms Nd:YAG laser for the removal of hair in subjects with Fitzpatrick skin types I-IV. Thanks to a pulse shorter than the hair Thermal Relaxation time (TRT), photothermolysis was thus achieved.

METHODS : This study assessed the percentage of hair reduction at 1 month and at 3 months after a single Nd:YAG laser treatment (Athos; Quantel Mdical, France); 3.5 ms pulse, single shot to 3 Hz, a maximum fluence of 80 J/cm 2 , 4 mm spot, no cooling system, no anaesthesia. The treatment sites consisted of three adjacent squares (optimum fluence, no treatment, -20% optimum fluence). Computerized hair counting was realized on digital pictures. The phototype, pain, side effects and patient's satisfaction were noted. Biopsies were performed 15 min after treatment. The enrolment consisted of 17 women, 22-60 years old, phototypes I-IV, with a follow-up at 1 month and 3 months of 25 sites.

RESULTS : Counting at 1 month and at 3 months revealed a significant hair reduction compared with the control sites: 60% at 1 month ( P < 0.001) and 24% at 3 months ( P < 0.05) for optimal fluence (25-80 J/cm 2 ), compared with 31% and 0% on the control sites; values similar to those published for Nd:YAG or diode lasers. There were no adverse effects at all. Biopsies showed lesions from necrosis coagulation of the root sheaths and hair disruption to isolated apoptotic cells in the outer root sheath, depending on the fluence applied.

CONCLUSION : Results from this study show that the Athos Nd:YAG is efficient and safe for removing pigmented hair in phototypes I-IV.