Specialists in the Medical & Psychological Aspects of Transgender Health Care 

Figure 1. Mean percentage of patient hair regrowth.

Patient subjective hair-density estimates reflected the objective hair count data (Figure 6). Full hair regrowth occurred in all study quadrants based on hair counts and patient hair-density estimates by the 6-month follow-up evaluation. Several patients, however, reported that their hair quality had changed after laser treatment, the regrown hairs exhibiting finer texture and lighter color.This change in hair quality could not be easily judged by photographic analysis and therefore could not be supported by objective data. Other than a transient folliculitis that developed in three wax-epilated test quadrants, no cutaneous pigmentary or textural complications developed after laser treatment.

Hair removal has become a major research interest and economic force within the field of cutaneous laser medicine. Laser systems with differing wavelengths, pulse durations and energy densities are currently under development for hair removal, based largely on unproven theories and vague mechanisms of action. While the theory of selective photothermolysis could be used to optimize wavelengths and pulse durations for laser epilation, the exact target within the hair follicle has yet to be clearly established? The hair matrix, papilla, and bulge are all potential areas of hair follicle vulnerability. However, without knowledge of a specific follicular target, it becomes difficult to predict which laser wavelengths and pulse durations will be most successful.

At the time of study initiation, only one laser-assisted hair removal device had been approved for use by the Food and Drug Administration [the SoftLight system by Thermolase Corp.]. This system uses energy from a Q-switched Nd:YAG laser following pretreatment wax epilation and application of a patented carbon-based topical solution. It provides an exogenous target chromophore [eg, carbon] to which 1064- nm-wavelength laser light has an affinity. The carbon is theoretically placed within wax-epilated follicles, and laser- induced thermal and photoacoustic damage is subsequently produced within the follicular structure. Selective damage, then, remains independent of the presence of endogenous melanin.

The results of this study suggest that after a single Q-switched Nd:YAG laser treatment, a change within the hair follicle is produced that results in a delay of hair regrowth. However, permanent hair removal [cessation of hair growth in treatment areas for the lifetime of the patient] was not achieved. All treatment sites exhibited full hair regrowth by six months, with some patients demonstrating regrowth as early as one and three months. While the ideal goal of laser- assisted epilation is permanence, the results of this study are consistent with those of previous studies involving single- session laser hair removal. Goldberg” reported that Q- switched Nd:YAG laser treatment and application of carbon solution provided a reduction in hair growth for up to six months. Grossman et al reported a delay in hair growth for a six-month period after long-pulsed normal-mode ruby laser irradiation. This apparent lack of permanence after laser hair removal has been disappointing, but not entirely unexpected, considering the vulnerability of hair to treatment at different phases in its growth cycle.

Repeated laser injury to the hair follicle, which was not examined in the current study, should be investigated. Future studies should also address the question of whether laser light simply induces a prolonged telogen hair cycle or whether irreversible follicular damage is possible. Ultimately, histologic examination of treated hirsute sites will be necessary to fully understand the mechanisms of laser-assisted hair removal.

Although pretreatment with wax epilation and a topical carbon solution resulted in significant hair removal, this protocol was not essential. All laser-treated sites showed less hair regrowth at three months than the wax-epilated control quadrants, suggesting that the laser energy can target the follicle without an exogenous carbon chromophore. However, because of the limited number of anatomic regions treated in this study, we lacked the statistical power to determine if a particular pretreatment protocol was superior to another.

It is interesting to note that the quadrants that were simply exposed to laser radiation without waxing or carbon solution did not show a significant reduction in hair growth until the third month. This finding may be attributed to the fact that, in areas that were not wax epilated, laser irradiation caused the terminal hairs to whiten but to remain in the follicles. Although the hair shafts were injured, hair counts at one month included these depigmented hair shafts. By the third month, however, the injured hairs had fallen out of the follicles and a significant reduction in hair counts was recorded.

While the results of this study suggest that wax epilation and/or carbon-based solution application is not essential to the laser-assisted hair-removal process, it is important to note that all study subjects had brown or black hair. When blonde or white hair-bearing areas are being treated, exogenous carbon pigment application may play a more important role in selectively targeting and concentrating laser energy into the follicle. Presumably, melanocytes and melanin within the hair follicle and shaft are the primary targets of Q-switched Nd:YAG laser energy when the laser treatment is used without a carbon solution.

These melanin-producing cells are located within the hair matrix at the base of the follicle, the infundibulum, and sparsely within the outer root sheath.(8,9) As there are greater numbers of melanocytes within the hair follicle than there are within the epidermis, laser energy can pass through the skin surface and be absorbed selectively by follicular melanin.(9) This selective process obviously becomes more problematic when lighter hair colors are being treated. Gray hair, for instance, has fewer melanocytes at the hair bulb, and blonde hair has a decreased number of partially pigmented melanosomes as compared with black hair.* Therefore, exogenous pigment in the form of a carbon-based solution may be helpful in the treatment of individuals with lighter hair colors.

In conclusion, a single treatment with a Q-switched Nd:YAG laser results in a greater delay of hair growth (up to six months) when compared with wax epilation alone. Regardless of the use of pretreatment wax epilation or carbon topical solution, hair growth was decreased when compared with control [waxed] areas. Complete hair regrowth occurred by six months after a single treatment, suggesting that further research is needed to determine the optimal treatment intervals, energy settings, wavelengths, and pulse durations needed to achieve longer-lasting or permanent laser-assisted hair removal.