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Laser Hair Removal: Study by Massachusetts Doctors

Effective, Long-term Hair Removal Using a Pulsed, High-Power Diode Laser
Christine C. Dierickx, MD(l); R. Rox Anderson, MD (l); Valeria B. Campos, MD(l); Melanie C. Grossman, MD(2)
Wellman Labs of Photomedicine, Harvard Medical School

The study summarized below was presented in progress to FDA. which cleared the LightSheerTM Diode Laser System for hair removal in December 1997. This summary is intended to allow users of this system to better inform their patients. This is not a peer-reviewed medical publication, and is provided by Coherent Medical solely for informational purposes regarding its products. It is not a substitute for clinical observation of laser-tissue interaction and clinical experience. Training is recommended prior to using the LightSheer Diode Laser System.

INTRODUCTION
A solid-state, 800 nm pulsed near-infrared diode laser was studied for long-term hair removal. The effect of laser fluence (energy per unit area), single vs. multiple treatments, and single vs. multiple pulses were determined in different skin types (Fitzpatrick's type I through VI). Semiconductor diode lasers are considered the most efficient light sources available and are particularly well suited for clinical applications. The pulsed diode laser used in the study delivers high-energy laser pulses, in combination with a proprietary skin cooling system, to target pigmented hair follicles deep within the dermis. Research and extensive clinical use of lasers for hair removal have identified important parameters to optimize the efficacy and safety of laser treatment:
  • Wavelength
  • Cooling
  • Fluence
  • Number of Treatments
STUDY DESIGN
The primary objective was to investigate effectiveness and safety of a pulsed diode laser in long-term removal of pigmented hair. This large, long-term, prospective, blinded, controlled and quantitative study was designed to study fluence-response relationship, one versus two treatments, and single versus multiple pulses. Ninety-two (92) patients were treated at two facilities: 46 patients at the Massachusetts General Hospital in Boston and 46 at the Laser and Skin Surgery Center of New York, in New York City. There were 45 males and 47 females with varying hair colors and skin types (Fitzpatrick's skin type I to VI; predominately II to III). All patients were treated and examined at 0, 1,3,6 and 9 months, and thirty-five patients were also followed up at 12 months.

The device used was a semiconductor diode laser system that delivers pulsed, infrared light at a wavelength of 800 nm, pulse duration from 5-20 ms and fluences from 15-40 J/cm2. The laser hand piece contains high-power diode arrays, eliminating the need for an articulated arm or fiber-optic beam delivery system. The handpiece contains an actively cooled convex sapphire lens that, when pressed against the patient's skin slightly before and during each laser pulse, provides thermal protection for the epidermis. Before each treatment, eight test sites were positioned on a patients.

An independent statistician performed data analysis. Hair reduction was defined as the percentage of terminal hairs absent after treatment, compared with the number before treatment. Hair reduction was quantified at each follow-up visit tar each site, and the mean hair loss and standard error were calculated.

RESULTS
Treatment demonstrated two different effects on hair growth: hair growth delay and long-term 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.

Hair regrowth stabilized at 6 months at all fluences; there was no further hair regrowth between 6, 9 and 12 months. This stabilizing of hair regrowth or hair count is consistent with the clinically accepted growth cycle of follicles and the definition of long-term term 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 regrowing hairs. Histological analysis suggested two mechanisms for effective, long-term removal 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.

CONCLUSIONS
The pulsed diode laser utilized in this study provides a safe and effective treatment that achieves both temporary and long-term reduction of unwanted, pigmented hair. Long-term hair reduction occurred in 89% of the patients in this large long-term, prospective, blinded, controlled and quantitative study. On average, about half of the hair had long-term removal after two treatments at a fluence of 40 J/cm2. Many patients had nearly complete, long-term hair reduction after two treatments, while a few had little or no long-term hair reduction. Regrowing hair is typically thinner and lighter in color, adding to the cosmetic benefit. Both the efficacy for hair removal and the risk of side effects increase with increasing treatment fluence.

Footnotes:
1. Now commercially available as the LightSheer Diode Laser System.
2. Pulse width setting for the system tested. Current system has a pulse width setting of 7.5 ms for 15 J/cm2.

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