Early Histopathological Changes Observed after Laser Treatment

In studies using various laser systems at varying fluences, coagulation of cellular proteins in hair follicles was observed after irradiation at high fluence levels. In skin samples biop – sied immediately after the normal-mode ruby laser pulses at fluence of 30-60 J/cm2, selec­tive but heterogeneous follicular damage was detected, consisting of thermal coagulation and asymmetric focal ruptures of the follicular epithelium. The presence of focal ruptures suggested vaporization and steam formation with temperature exceeding 100°C in some areas of the follicle [58]. In another study, ruby laser at a fluence of 11 J/cm2 caused wide­spread coagulation and charring of subcutaneous hair shafts, as well as distortion and crack­ing of the shaft matrix [52]. A study by Kato T et al. (2004), also with the ruby laser showed localized damage in the hair bulb and the bulge region, and dilation of the inner root sheath filled with eosinophilic substances [59]. Exposure of the hair follicles to 11-17 J/cm2 alex­andrite laser resulted in the disappearance of inner root sheath cells and disruption in the cellular polarity of the outer root sheath and dermal papilla [59]. Coagulation of hair follicle components was also observed with alexandrite and diode laser systems at 25-40 J/cm 2 immediately following irradiation, and accompanied by variable amounts of inflammation and pigmentary changes [60]. Similar findings were reported by Ono and Tateshita (2000) who observed histopathological changes in melanin-containing cells, including damaged external root-sheath and swollen dermal papilla after exposure to long-pulsed alexandrite laser at fluence of 25 J/cm2 [16]. Extensive necrosis of follicular and sebaceous gland epi­thelium was evident in the specimen obtained 6 h after treatment with Nd-YAG laser at flu­ence of 23-56 J/cm2 [61]. The laser-induced damage to follicular cells was most often seen associated with the damaged hair shafts [13]. Collectively, these studies provide evidence in support of thermal-induced injury not only to the melanin rich follicle structures, but also to the surrounding cellular components including epithelial cells of the inner and outer root sheaths, and in some instances, the cells of dermal papilla.