Summary provided by Lumenis, 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 Lumenis Inc.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 laser1 was studied for permanent hair reduction. 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-power laser pulses, in combination with a proprietary skin coolingsystem, 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 twoimportant anatomical targets for inactivation of hair follicles: 1) stem cells in a “bulge” 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 oflaser treatment: • Wavelength: Most laser hair removal systems are designed to remove unwanted hair through selective photothermolysis. This process involves local selective absorption of an intense light pulse at wavelengths that: 1) are preferentially absorbed by the desired hair follicles but not by the surrounding tissue; and 2) penetrate deeply into the skin to reach the important targets forinactivation of hair follicles. In laser hair removal, the most important and dominant absorber is melanin. In all colors but white hair, there is sufficient melanin in the follicular epithelium and matrix to act as a chromophore for light absorption in the follicle. Laser energy is selectively absorbed by the melanin and causes thermal damage to the hair shaft and follicle. Hair growth is impededor eliminated with sufficient fluence of the appropriate wavelength, due to selective thermal damage of the hair follicle. The ideal laser wavelength for hair
removal is strongly absorbed by melanin but not by surrounding tissue and reaches deeply into the dermis. Wavelengths between about 700 and 1000 nm fit these criteria. • Pulse Width: Pulse width is a very important parameter for effectivelaser hair removal without epidermal injury. For hair removal, the optimum pulse duration is approximately equal to the thermal relaxation time (TRT) of the hair follicle. The TRT is defined as the time required for an object to cool to half the temperature achieved immediately following laser exposure. For human terminal hair, TRT varies from about 10 to 100 milliseconds. Laser pulses muchshorter than the TRT cause insufficient heating of the target structures (bulb and papilla) surrounding the hair shaft. Pulse widths much longer than the TRT may cause non-selective damage to the surrounding dermis. The first laser hair removal treatment to be cleared by FDA used Nd:YAG laser pulses about a million times shorter than TRT for hair follicles, and failed to produce long-term hair...