Abstract:

Objective To investigate the histological changes of normal human skin after fixed irradiation with multiple-pulse fractional Er:YAG laser. Methods After hair removal, the upper arms of 7 healthy volunteers were consecutively irradiated with multiple-pulse fractional Er:YAG laser. Tissue samples were resected from the irradiated skin at 1, 24, 48, 72 hours, on day 5, 7, 15, and 30 after the irradiation. Hematoxylin and eosin （HE） staining and Masson staining were performed to observe the histological changes and collagen proliferation respectively. Immunohistochemical staining was used to detect the expression of heat shock protein （HSP） 70 and 47. Results The consecutive irradiation with multi-pulse fractional Er:YAG laser generated an array of tapering microscopic treatment zones（MTZs） of gasification and ablation in the upper arm skin. After the irradiation, inflammation developed in the microscopic lesions with the epithelization of epidermal cells within 7 days; local dermal collagen was renewed and remodelled during the 7th to 30th day. HSP70 expression peaked as early as 48 hours after the treatment and maintained until the 7th day, while the high expression of HSP47 persisted from the 15th to 30th day after irradiation. Conclusion The fixed, multiple-pulse and fractional Er:YAG laser irradiation can reach the deep dermis, and induce the local proliferation of dermal collagen.

Key words: collagen