Effective, Permanent Hair Reduction Using a Pulsed, High-Power Diode Laser
Christine C. Dierickx, MD*; R. Rox Anderson,
MD*; Valeria B. Campos, MD*; Melanie C. Grossman, MD** *Wellman Labs
of Photomedicine, Harvard Medical School
Summary provided by Coherent Medical, Inc.
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.
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-power laser pulses, in combination with a proprietary skin cooling system, to target pigmented hair follicles deep within the dermis. Treatment operates on the principle of selective photothermolysis, which combines selective absorption of light energy by the melanin in hair follicles with suitable pulse energies and pulse widths (pulse duration) that are equal to or less than the thermal relaxation time (TRT) of targeted follicles in human skin. There are two important anatomical targets for inactivation of hair follicles: 1) stem cells in a ìbulgeî of the outer root sheath about 1 mm below the skin surface; and 2) the dermal papilla located at the deepest part of the follicle, which varies with hair growth cycle. Research and extensive clinical use of lasers for hair removal have identified important parameters to optimize the efficacy and safety of laser treatment:
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 (Fitzpatrickís 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. Testing with diode lasers has shown that at 800 nm, the laser light effectively penetrates the dermis, where follicular melanin is the dominant chromophore. Given that the thermal relaxation time for hair follicles ranges from 10-100 ms, the pulse duration of 5-20 ms produced by this device is long enough to allow heat conduction from the pigmented hair shaft during each pulse.
The laser handpiece contains high-power diode arrays, eliminating the need for an articulated arm or fiber-optic beam delivery system. The handpiece integrates a condenser thatmixes light to produce a fluence of 15-40 J/cm2 over a uniform 9x9 mm area. The handpiece contains an actively cooled convex sapphire lens that, when pressed against the patientís skin slightly before and during each laser pulse, provides thermal protection for the epidermis. The cooling lens not only allows higher doses of laser energy to safely and effectively target hair follicles, but also allows compression of the target area placing hair roots closer to the laser energy.
Before each treatment, eight test sites were positioned on a patientís thigh or back with two micro-tattoos or other anatomic landmarks to ensure exact location of the test sites at follow-up visits. Hairs at each site were trimmed to a uniform length using clippers, and the skin was cleaned with isopropanol. Digital images of the treatment sites were taken at the initial visit and at each follow-up visit (1, 3, 6, 9 and 12 months). A charge-coupled-device video camera with a photographic ring flash and frame-grabber was used to provide high-resolution hair imaging. The camera was connected to a computer with image acquisition hardware and image analysis software. The number of hairs was counted blindly in each test area before laser treatment, and at each follow-up visit.
The exposure schedule for the eight treatment sites is shown in Table 2. The fluence range tested was 15-40 J/cm2 and the pulse duration was 5-20 ms. At those sites receiving two treatments, exposure was repeated one month after the first treatment. At sites receiving multiple pulses, three pulses were applied to the same area, two seconds apart. All patients also had a control site that was unexposed and shaved.
Clinical evaluation of results and CCD imaging were conducted at 0, 1, 3, 6, 9, and 12 months after treatment. Approximately 4,000 images were analyzed during this study. Investigators visually assessed skin response, including hypopigmentation, hyperpigmentation, erythema, edema and textural differences, using a response grading scale of 0-3 (none/absent to full/severe). Hair count, hair phase, growth rate, and shaft diameter were quantified using the digital images. Biopsies were also taken at sites with obvious laser-induced hair loss, at different times after exposures, and were processed and examined by light microscopy.
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 for each site, and the mean hair loss and standard error were calculated.
Table 4 shows percentage of hair reduction for all sites for all laser configurations. After two treatments at 40 J/cm2 (20 ms pulse duration)3, the average permanent hair reduction 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 one month later removed an additional 25%. Triple-pulsing (3x) did not significantly increase hair reduction over single pulsing, after one or two treatments. However, the incidence of side effects was higher for triple pulsing.
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 (Table 5) and 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.
Statistically significant reduction in average hair regrowth (p<0.01) continued at 3, 6, 9, and 12 months for all sites, at all fluence-pulsewidth configurations, after both one and two treatments. Eighty-nine percent of patients exhibited significant permanent hair reduction at all configurations.
In addition to statistically significant hair reduction, treatment with the laser also showed reduction in hair diameter and reduction in color of regrowing hairs. Regrowing mean hair diameter decreased by 19.9%, and optical transmission at 700 nm of hair shafts regrown post-treatment was 1.4 times greater than transmission pretreatment (p<0.05). These added benefits of the treatment are cosmetically desirable, since thinner, lighter hairs add to the appearance of hair reduction.
Histological analysis suggested two 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. The histological examination in this study showed that treatments with the pulsed diode laser caused immediate thermal damage in follicles with large, pigmented shafts, while 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. Histological analysis also demonstrated that triple pulsing did not produce more follicular damage than single pulsing, although the dermis between closely spaced follicles was occasionally injured by triple-pulsing. Sebaceous glands near the treated follicles showed no or minimal thermal damage, and sweat glands and dermal capillaries appeared normal.
This study was intended to elicit side effects, by covering a wide range of fluences, regardless of skin type. 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 fluence given 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 large areas.
Immediately after treatment, the typical
response is perifollicular erythema and edema, which subsides within a
few hours. In this dose response study, all fluences were given to most
patients, regardless of skin type. (At the New York site, fluences at
or above those that showed evidence of epidermal injury were not delivered.
This resulted in several
On average, about half of the hair had permanent hair reduction after two treatments at a fluence of 40 J/cm2. Many patients had nearly complete, permanent hair reduction after two treatments, while a few had little or no permanent 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. There was an apparent threshold fluence for inducing side effects in each skin type.
The mechanisms for permanent hair reduction include miniaturization of terminal hairs, and degeneration of follicles damaged by selective photothermolysis.These study results support the clinical utility of the high-power, pulsed diode laser as a safe and effective device for permanent reduction of pigmented, terminal hair.
In clinical practice, fluence and pulse width should be adjusted for skin type. At one clinical location over 1,000 clinical treatments were performed with this device, in which fluence and skin type were matched to optimize the efficacy and safety of treatment. When this was done, the incidence of side effects was less than 1%, and was limited to transient changes in skin pigmentation.
2Pulse width setting for the system tested. Current system has a pulse width setting of 7.5 ms for 15 J/cm2
3A lower fluence is recommended until
significant experience is obtained with the LightSheer. Please contact
your Coherent sales representative for a copy of Recommended Guidelines
for Treating Patients for more
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