Abstract: Objective To evaluate the clinical efficacy,safety and recurrence rate of picosecond 755 nm alexandrite laser in the treatment of melasma.Methods All 51 patients with melasma were treated with picosecond 755 nm alexandrite laser combined with a focus lens array for 5 treatment sessions every 3 weeks.The treatment parameter:0.4 J/cm2 of fluence,8 mm of spot size,5 Hz of frequency and 550×10-12 sec of pulse duration.Patients were all followed up for 8 weeks.Outcomes assessments including photography,melasma area and severity index (MASI) score and related adverse reactions were recorded.The factors affecting the treatment were analyzed.Results The mean MASI score decreased dramatically from (12.04±6.54) to (6.82±5.63) after 5 laser treatment sessions,the decreasing ration of the MASI score was about 47.22％.But after 8-week follow up,the mean MASI score slightly increased to (7.67±5.63).No obvious side effect was observed.Through the statistical analysis,disease duration,severity,wood's lights typing,Fiztpatrick typing,and family history of melasma had impact on the prognosis of melasma.Conclusion The novel picosecond 755 nm alexandrine laser is effective and safe with lower recurrence rate in the treatment of melasma,and is worthy of promotion.

Key words: Picosecond alexandrite laser, Melasma, Treatment assessment