Clinical Studies

Diode lasers emit 800 nm laser light. These systems are among the newest available hair removal lasers. Dierickx, Grossman and others3 evaluated the effectiveness and safety of a pulsed diode laser in the permanent reduction of unwanted hair. Ninety-five subjects were evaluated. Different hair colors and skin types (Fitzpatrick’s skin types II to VI) were treated. The majority had Fitzpatrick II–III skin phenotypes and brown or black hair. Subjects were treated and examined at baseline, 1, 3, 6, 9, and 12 months after treatment. The objective of the study was not only to investigate effectiveness and safety of a pulsed diode laser in the permanent reduction of pigmented hair, but also to study the fluence–response relationship. The authors also evaluated 1 versus 2 treatments, and single versus multiple pulse treatments of the same area. The device used was a semiconductor diode laser system that delivers pulsed, infrared light at a wavelength of 800 nm, pulse duration from 5 to 20 msec and fluences from 15 to 40 J/cm2. In this study, the laser handpiece contained a high-power diode array, eliminating the need for an articulated arm or fiber-optic beam delivery system. Laser energy was delivered over a 9 × 9 mm area. The handpiece contained an actively cooled convex sapphire lens that, when pressed against the subject’s skin slightly before and during each laser pulse, provided thermal protection for the epidermis. The cooling lens allowed not only higher doses of laser energy to be safely and effectively delivered, but also permitted compression of the target area, placing hair roots closer to the laser energy. Treatment results demonstrated 2 different effects on hair growth: hair growth delay and permanent hair reduction. A measurable growth delay was seen in all patients (100%) at all fluence/pulse width configurations tested; this growth delay was sustained for 1–3 months. Significant fluence-dependent, long-term hair reduction occurred at all fluences in 88% of subjects. Clinically obvious long-term hair reduction usually required >30 J/cm2. After two treatments at 40 J/cm2 with a 20 msec pulse duration, the average permanent hair reduction at the end of the study was 46%. Two treatments significantly increased hair reduction as compared to one treatment, with an apparently additive effect. At a fluence of 40 J/cm2, the initial treatment removed approximately 30% of terminal hairs, and the second treatment given 1 month later removed an additional 25%. Triple pulsing of the same area did not significantly increase hair reduction over single pulsing, after 1 or 2 treatments. However, the incidence of side effects was higher for triple pulsing. Of note, hair regrowth stabilized at 6 months at all fluences; there was no further hair re-growth between 6, 9, and 12 months in this study. This stabilizing of hair re-growth or hair count is consistent with the clinically accepted growth cycle of many hair follicles. It is also consistent with the definition of permanent hair reduction, being a significant reduction in the number of terminal hairs after treatment, which is stable for a longer period than the complete growth cycle of follicles at the body site tested. In addition to statistically significant hair reduction, treatment with the laser also showed reduction in hair diameter and reduction in color of re-growing hairs. Re-growing mean hair diameter decreased by 19.9%. Optical transmission at 700 nm of hair shafts re-grown post-treatment was 1.4 times greater than transmission pre-treatment. Said differently, the hairs remaining after treatment were lighter and thinner. Histologic analysis suggested 2 mechanisms for effective, permanent reduction of terminal hair: miniaturization of coarse hair follicles to vellus-like hair follicles, and destruction of the follicle with granulomatous degeneration with a fibrotic remnant. Immediately after treatment, hairs show evidence of thermal damage in follicles with large, pigmented shafts. Follicles with small vellus shafts showed no effect. Both pigmented and non-pigmented areas of terminal hair follicle epithelium showed thermal coagulation necrosis, with minimal or no damage to the adjacent dermis. Triple pulsing did not produce more follicular damage than single pulsing, although triple pulsing occasionally injured the dermis between closely spaced follicles. Sebaceous glands near the treated follicles showed no or minimal thermal damage. Sweat glands and dermal capillaries appeared normal.
As would be expected from any visible light, melanin-absorbing system, side effects with pulsed diode laser treatment were fluence and skin type dependent. Hyper- or hypopigmentation was minimal in fair skin, and increased with fluence and with darker skin type. At the highest delivered fluence of 40 J/cm2, the incidence of hyper- or hypopigmentation was greater for patients with skin types III through VI. In addition, clinical experience has shown that these high fluences may elicit somewhat greater side effects in treatments of areas of high hair density.
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