Immunohistological Evaluation of Skin Responses After Treatment Using a Fractional Ultrapulse Carbon Dioxide Laser on Back Skin

BACKGROUND AND OBJECTIVE Fractional photothermolysis (FP) lasers have been widely used in treating photo‐aged skin, acne scars, and other skin conditions. Although plenty of clinical data have demonstrated the efficacy of the FP laser, only limited histologic studies have been available to observe serial short‐ to long‐term skin responses. METHODS Seven healthy Chinese women received one pass of fractional carbon dioxide laser treatment on the left upper back. Biopsies were taken at the baseline and 4 hours, 1 day, 5 days, 1 month, 3 months, 6 months, and 1 year after the procedure for hematoxylin and eosin stains, immunohistochemical evaluation (for heat shock proteins and elastin), and Verhoeff‐iron‐hematoxylin stains (for collagen and elastic fiber). RESULTS Remarkably greater expression of heat shock protein (HSP)70 could be observed 4 hours after the procedure, which diminished significantly by 3 months, 6 months, and 1 year after the procedure. HSP47 reached its peak expression 1 month after the procedure, especially around microscopic thermal zones, and maintained its high level of expression 3 and 6 months after the procedure. Distinct new formation and remodeling of collagen and elastic fibers could be observed 3 and 6 months after procedure. CONCLUSION FP‐induced HSP expression and new formation of collagen and elastic fibers lasted as long as 6 months, longer than the previously acknowledged 3 months. The authors have indicated no significant interest with commercial supporters.