Vascular mechanisms in laser hair removal

To the Editors, There is no doubt that permanent hair removal or reduction by means of lasers has received tremendous media and public attention. Unfortunately, initialÐ largely unsubstantiatedÐclaims fueled public expectations far exceeding the technical capabilities of these systems. Recent research efforts have attempted to better de®ne the role of lasers in the process of hair removal. These studies have examined factors such as wavelength, pulse duration, ̄uence, hair color, growth stage and active and passive cooling in an attempt to improve clinical ef®cacy and limit post operative side effects. The microscopic anatomy of the hair follicle has been well described. Two structures appear to play a role in hair growth and regeneration. The dermal papilla controls follicular growth, function and differentiation. The bulge area may carry the stem-cell capacity for follicular regeneration. Histologic studies of anagen follicles treated by means of laser show coagulative necrosis of the dermal papilla and hair shaft with surrounding thermal damage to the root sheaths and perifollicular tissue (Figure 1). In an attempt to further elucidate mechanisms involved in laser hair removal, we studied biopsies from sites treated using long-pulsed Alexandrite 755 nm, Diode 810 nm, and long-pulsed Nd:YAG 1064 nm lasers. All of these systems are capable of signi®cant widespread destruction of anagen follicles (Figure 2). In addition, higher ̄uences were associated with marked perifollicular damage, particularly at the base of the follicles surrounding the dermal papilla. Three distinct responses may be seen in follicles exposed to laser radiation of suf®cient ̄uence and of proper wavelength miniaturization of follicles, decreased pigmentation of regrowing hair and degeneration of follicles with ®brosis. Although most investigators have focused on the bulb and bulge as the target for laser hair