Department of Plastic Surgery, Tokai University, Kanagawa, Japan.
Cosmetic Laser Dermatology, San Diego, CA, USA.
Lasers Med Sci. 2022 Dec;37(9):3613-3619. doi: 10.1007/s10103-022-03640-x. Epub 2022 Sep 1.
The safety and efficacy of laser hair removal have been well established through many clinical studies and through clinical use over the past 25 years. A laser hair removal device that protects the epidermis by utilizing cryogen spray cooling (CSC) is widely used internationally. In darker skin types, post-inflammatory hyperpigmentation (PIH) can occur after laser hair removal. In particular, laser hair removal with CSC is known to cause crescent-shaped or ring-shaped PIH. In this experiment, we report a visualization of this PIH mechanism. The laser used in this experiment is a 755-nm-long-pulsed alexandrite laser. Graph paper was treated with this laser to assess for thermal damage. We investigated changes in thermal damage due to differences in laser spot size, fluence output, and laser beam angle in relation to the graph paper. When using a spot size of 18 mm, we observed that higher fluences caused crescent-shaped thermal damage on the margins of the treated graph paper. It was also confirmed that when the hand piece is not held perpendicular to the skin, the laser-treated area is expanded and the CSC range is narrowed. These factors caused the area of thermal damage to widen. This widening causes ring-shaped thermal injury, leading to PIH. We treated graph paper using a hair removal laser with CSC to investigate the mechanism of crescent or ring-shaped thermal damage. Laser treatment on graph paper is effective as a test for defects in the CSC device. Factors that cause inadequate cooling, which leads to PIH, are large spot size, high fluence, not holding the laser hand piece perpendicular to the skin, and malfunctioning of CSC device.
激光脱毛的安全性和有效性已通过许多临床研究和过去 25 年的临床应用得到充分证实。一种通过利用制冷剂喷雾冷却（CSC）来保护表皮的激光脱毛设备在国际上得到广泛应用。在肤色较深的人群中，激光脱毛后可能会出现炎症后色素沉着过度（PIH）。特别是，带有 CSC 的激光脱毛已知会导致新月形或环形 PIH。在这项实验中，我们报告了这种 PIH 机制的可视化结果。本实验中使用的激光是一种 755nm 长脉冲翠绿宝石激光。用这种激光处理格纸，以评估热损伤。我们研究了由于激光光斑大小、能量密度输出和激光束角度与格纸的不同而导致的热损伤变化。当使用 18mm 的光斑时，我们观察到较高的能量密度会在处理过的格纸边缘造成新月形的热损伤。还证实了当手持件未垂直于皮肤时，激光处理区域会扩大，CSC 范围会变窄。这些因素导致热损伤区域扩大。这种扩大导致环形热损伤，从而导致 PIH。我们使用带有 CSC 的脱毛激光处理格纸，以研究新月形或环形热损伤的机制。用激光处理格纸是测试 CSC 设备缺陷的有效方法。导致冷却不足从而导致 PIH 的因素包括：光斑过大、能量密度过高、手持件未垂直于皮肤以及 CSC 设备故障。
