Efficacy and Safety Comparison Between Fractional 2940nm Er:YAG Laser and Fractional 1927nm Thulium Laser in the Treatment of Facial Atrophic Acne Scars

Acne vulgaris is a chronic and recalcitrant inflammation of pilosebaceous unit that has a high incidence rate in adolescence and even adults. Acne scarring is not an uncommon cosmetic complication which will cause physical and phycological pressure and impair the life quality of patients. It can be divided into two types according to morphology: atrophic and hypertrophic acne scarring. Atrophic acne scarring can be subclassified into boxcar, icepick and rolling scarring due to morphological features. Although a great variety of modalities to treat atrophic acne scarring such as chemical peeling, lasers and light, micro-needling and radiofrequency have emerged, fractional laser (FL) have come out on top. Unlike resurfacing lasers, FL creates three-dimensional, evenly distributed "microscopic thermal zones(MTZs)"on the treating area, which only covering about 3-40% of the skin and leaving the surrounding tissue undamaged and serving as "cell reservoir". Then, the MTZs can be rapidly replaced by keratinocytes in "cell reservoir" within the first 24 hours and by new collagen within 3-6 months. FL can be categoried into fractional ablative laser(FAL) and fractional non-ablative laser(FNAL).

With a wavelength of 2940nm, FEL could be highly absorbed by water-containing tissues of skin and cause superficial epidermis ablation and collagen induction[4]. But thermal damage is limited to about 20-50um. FTL has a moderate affinity for water content tissue. Thus, rather than causing epidermis turnover, it keeps the epidermis intact. But it can penetrate deep into 200-300um and stimulate collagen regeneration. Prior studies have shown that both FAL and FNAL were effective in treating acne scarring and the former were more effective while the latter had less side effects. However, in our clinic, we have observed outstanding effect and high satisfaction rate of FTL in improving atrophic acne scarring. Since there was only one clinical trial reported the efficacy and safety of FTL in Asian and no study have made a comparison between FTL and FEL, we designed this prospective, simultaneous spilt-face trial, hoping to provide a new available modality for patients who are intolerable or reluctant to ablative lasers.