Effects of the 1,320-nm Nd:YAG laser on transepidermal water loss, histological changes, and collagen remodeling in skin.

The goal of the study is to investigate the effects of the 1,320-nm Nd:YAG laser on skin barrier function and dermal remodeling. Forty-eight female mice were irradiated with the 1,320-nm laser four times at an interval of 1 week (350 micros, 10 mm, single pass 10% overlap). Three doses were used: 18, 22, and 26 J/cm2. Transepidermal water loss (TEWL) was measured at day 0, 1, 7, 21, 30, and 60 after treatments. Skin biopsies were taken to observe the changes in dermal structures and quantify the increases in the number of fibroblasts and collagen content. The dose of 22 J/cm2 induced the lowest ratio of TEWL (0.58+/-0.06, p < 0.05), highest degree of fibroblast proliferation (45.68+/-5.70, p < 0.05), and the most increase in type I collagen fibers (49.8%, p < 0.05) and hydroxyproline content (85.7%, p < 0.05). The dose of 26 J/cm2 caused marked inflammatory infiltration and the most increase in type III collagen fibers. The increase of type I collagen fibers was greater than type III collagen fibers for all three doses (p < 0.05). Our results demonstrated that 22 J/cm2 was most effective in enhancing skin barrier function and stimulating new collagen synthesis. Dermal remodeling after the 1,320-nm laser was mainly through the synthesis and deposition of collagen type I. Inflammatory reactions were in favor of the formation of type III collagen.