Several laser products have been commercialized for hair removal, but their efficacy has been questioned. Dierickx and associates evaluated the permanence of hair removal by normal-mode ruby laser treatment. This study was a two-year follow-up assessment of subjects in a previous study of a single laser treatment for hair removal on the thighs and backs of 13 volunteers.
The current study included seven of the original 13 participants. Baseline hair counts were obtained from eight test sites on each subject, and before laser exposure, one half of the test sites were shaved and one half were epilated with cold wax. Sites were irradiated with a normal-mode ruby laser at fluences of 0 (unexposed control), 30, 40 and 60 J (joules) per cm2. Terminal coarse hair counts were performed one, three, six, 12 and 24 months after laser exposure.
Follow-up revealed that four of the seven subjects still exhibited hair loss in the laser-treated sites two years after treatment; three had complete or nearly complete hair regrowth. All seven subjects showed no significant change in terminal hair counts six months, one year and two years after laser exposure, suggesting that six months' follow-up may be sufficient for assessing the outcome after laser therapy for hair removal. Neither pigment changes nor scarring was noted in any subject at the one-and two-year follow-up visits.
Sites treated with the highest laser fluence had the greatest hair loss. Compared with shaved and epilated control sites, laser-treated sites demonstrated significant hair loss at six months for all fluences at both shaved and epilated sites. At one- and two-year follow-up, significantly less hair appeared only in the shaved sites for all fluences compared with the untreated control site.
Terminal and vellus-like (miniaturized) hairs were examined histologically. The total number of hairs was identical in the control and laser-treated sites. However, in the laser-treated sites, a reduction in large terminal hairs and a reciprocal increase in small vellus-like hairs had occurred. The average hair shaft diameter measured on histologic sections also decreased after laser treatment. There were no signs of fibrous tracts, and normal-appearing sebaceous glands were still present around the villus hairs.
The findings indicate that permanent loss of terminal hair can result from a single exposure to high-fluence ruby laser therapy. The pulses generated by this particular laser were long enough to cause thermal coagulation and vaporization injury of hair follicles, leading to a growth delay in all subjects and permanent hair loss in some. This study suggests that the most important factor producing laser-induced alopecia is miniaturization of coarse terminal hair follicles to vellus-like hair follicles, resulting in finer and softer hair.
The authors hypothesize that two responses occur after laser treatment: a delay in hair growth and permanent hair loss. They postulate that the sensitivity of hair follicles to laser pulses may vary with the hair growth cycle. Hairs resistant to permanent inactivation may be in the telogen stage at the time of treatment.
editor's note: In an accompanying editorial, Tope notes the difficulty of obtaining accurate data on the efficacy of hair removal methods. Many studies have been based on clinical observations or patient satisfaction, without good follow-up data. Although the number of patients in this study was small, this study represents an attempt to define the safety and efficacy of hair removal by the pulse laser. This method may offer women with androgen-excess syndromes hope for permanent hair removal, which has been impossible to achieve with other therapies.—b.a.