Histological Characteristics of Skin Treated With a Fractionated 1064‐nm Nd: YAG Picosecond Laser With Holographic Optics

Background and Objectives Picosecond lasers (PSL) constitute a significant technological advancement and exert rejuvenating effects upon the skin. This study was conducted to investigate changes in the skin upon treatment with the fractionated 1064‐nm Nd: YAG PSL through in vivo and ex vivo human histological analysis. Study Design/Materials and Methods In vivo back skin specimens were treated with a fractionated 1064‐nm PSL at 1.3, 2.1, and 2.9 mJ fluence for two passes, and 2.9 mJ for 10 passes, and then stained with hematoxylin and eosin (H&E). Ex vivo foreskin specimens after circumcision surgery were treated with a PSL at 1.3, 2.1, and 2.9 mJ fluence for two and 10 passes, followed by H&E staining. Ex vivo skin tissue sections treated with a PSL at 2.9 mJ fluence for 10 passes were also immunostained for Melan‐A and CD31. Results Intraepidermal vacuoles were observed, along with pigment accumulation and inflammatory cell infiltration in the vacuoles at 24 hours after PSL treatment in the in vivo skin specimens. The vacuoles expanded as the fluence increased. Numerous intraepidermal vacuoles were observed, with dermal hemorrhage and inflammatory cell infiltration upon high‐fluence, multi‐pass PSL treatment in the in vivo skin specimens. PSL treatment yielded both epidermal and dermal vacuoles in ex vivo skin specimens. Melan‐A‐positive cells were seen in the cystic wall of vacuoles in the epidermal basal layer, whereas CD31‐positive cells were detected in the cystic wall of some dermal vacuoles. Conclusions The fractionated 1064‐nm PSL produced epidermal vacuoles and dermal lesions, with histological differences between the in vivo and ex vivo skin specimens. Lasers Surg. Med. © 2021 Wiley Periodicals LLC