Destruction of Follicular Stem Cells During Laser Hair Removal

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Destruction of Follicular Stem Cells During Laser Hair Removal
1/12/2007
Graeme Lipper, MD
Medscape Today

Summary

Since its initial description in 1986,[1] laser hair removal (LHR) has become the most popular cosmetic laser treatment worldwide, enjoying the reputation of being a safe, highly effective gold standard method for permanent hair removal. Although LHR has been postulated to act through the thermal destruction of follicular stem cells located in the bulge region of the hair follicle,[2,3] this has never been proven.

In a small prospective study, Orringer and colleagues studied the effects of LHR on the immunohistochemical staining patterns of human hair follicles, including the putative stem cell-containing bulge region. Subjects (n = 12; mean age, 39.8 years) with dark axillary hair were enrolled to receive single treatments with either a 1064-nm neodymium:yttrium-aluminum-garnet laser (1064-nm Nd:YAG) or 800-nm diode laser -- both popular choices for LHR in variable skin phototypes. The investigators used typical laser parameters that are known to produce permanent hair removal for both devices (diode: 12-mm x 12-mm spot size, 40-J/cm2 fluence, 20-ms pulse duration, contact cooling; Nd:YAG: 12-mm spot size, 50- to 70-J/cm2 fluence, 3-ms pulse duration, dynamic cooling device). The clinical efficacy of these treatments was judged to be good, although no formal hair counts were made before or after treatment.

Following the laser procedure, skin biopsy samples were taken for immunohistochemical analysis on days 1, 3, and 7. These specimens showed either thermal alteration or absence of the hair shafts; the hair bulbs (matrix and dermal papillae) remained intact at all time points, with variable focal alteration and/or disruption of the internal and external root sheaths. In contrast to these histologic changes, the immunohistochemical staining of the hair follicles remained relatively unchanged after laser irradiation. Specifically, staining for the immunohistochemical markers of multipotent (stem) cells in the bulge region (cytokeratins 15 and 19) stained with a similar pattern and intensity before vs after laser treatment.
Viewpoint

That permanent hair removal can be achieved following irradiation with melanin-selective lasers is a proven fact that has been demonstrated for many visible and infrared devices.[1,3,4] Prerequisites for permanent LHR include adequate melanin absorption (determined in part by laser wavelength, pulse duration, and spot size), the presence of a melanized hair shaft within the hair follicle, and sufficient energy (fluence) to achieve some "threshold level" of thermal injury to the targeted hair follicle. Although investigators have postulated that follicular stem cell damage is needed in order to achieve permanent hair removal, the observations of Orringer and colleagues call this notion into question.

These observations, although intriguing, do not offer any firm conclusions. If follicular stem cells are indeed altered following LHR treatment, such changes may be subtle and physiologic and not reflected in gross immunohistochemical staining patterns. One should also question whether Orringer and colleagues used the optimal staining techniques, because viability staining might have shown postlaser cellular injury not detected by cytokeratin staining alone. Finally, as the investigators acknowledge, their histologic analysis was conducted in the acute injury phase following laser irradiation (days 1-7), and the study was not designed to detect any long-term changes in stem cell viability or changes resulting from repeated laser injury.