The temperatures reached and the damage caused to hair follicles by the normal-mode ruby laser when used for depilation

Although it is proposed that heat is the cause of follicular damage leading to depilation, this has never been proved. This study aims to determine the mode by which depilation is effected and, if heat is the mechanism, what temperatures are reached within treated follicles and if sufficient damage is produced therein. Two excised specimens of hair-bearing skin from 5 patients undergoing facelifts were dissected to reveal the hair bulbs/shafts on the deep surface. They were placed on a jig, and one pulse from a normal-mode ruby laser (NMRL) of 15 J per square centimeter was fired on the epidermal surface. A thermal imaging camera recorded dermal temperature changes on the deep surface in real time. Specimens were then examined histologically for the site and extent of cellular damage by immunohistochemical staining for a protein marker of cell damage (p53). The NMRL targeted hair follicles specifically. The most common follicular temperature increase ranged from 5 to 10 degrees C. In specimens from 1 patient the increase was more than 30 degrees C (p < 0.001). Heat dissipation into interfollicular tissue in all specimens occurred 2 seconds after exposure. Evidence of laser-induced damage to follicle-lining cells was found only in those follicles with damaged hair shafts. The changes were found to a greater depth (to the bulb) and greater extent (beyond the bulge) in those follicles reaching higher temperatures. These findings suggest that the NMRL should produce permanent depilation. The variability between follicles and between patients explains, perhaps, the uneven outcome regarding depilation using the NMRL. Success appears to depend on peak follicular temperatures achieved during laser exposure, which may result from the follicular characteristics of the individual patient.