Evaluation of a New Super-Long-Pulsed 810 nm Diode Laser for the Removal of Unwanted Hair: The Concept of Thermal Damage Time

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Abstract
Background. Laser hair removal is based on the dual concepts of selective photothermolysis and thermal relaxation time. In most laser hair removal systems, light with emitted pulse durations of 2–50 msec targets hair follicles. A novel concept of laser hair removal uses the thermal damage time rather than the thermal relaxation time of the hair follicle. The follicle's thermal damage time is the amount of time required for diffusion of delivered laser energy from the treated hair to follicular‐associated hair stem cells. This can range from 170 to 1000 msec. objective. To investigate the theory of thermal damage time, we performed a pilot study to evaluate the clinical efficacy and side effect profile of a modified 810 nm diode laser device operating in a super‐long‐pulse mode (200–1000 msec). methods. Ten female subjects with Fitzpatrick skin types I–VI received either one or two laser treatments at eight test sites. Super‐long pulse durations of 200–1000 msec were evaluated with delivered fluences ranging from 23 to 115 J/cm2. Subjects were followed for 6 months after the first treatment. Subjects were evaluated for hair removal efficiency, optimal pulse duration and delivered fluence, and associated complication rate. results. The clinical results show that safe hair removal in all skin types can be accomplished with an 810 nm diode laser delivering super‐long pulse durations. Pain and complications were greatest at the highest pulse duration (1000 msec) and the highest fluence (115 J/cm2). Optimal hair reduction at 6 months (31%) was achieved at a thermal diffusion time of 400 msec (46 J/cm2). conclusion. The super‐long pulsed 810 nm diode laser can safely remove unwanted hair in a full variety of skin types. Pain and increased risk of complications may preclude the use of the laser at very high fluences and pulse duration in the range of 1000 msec.