Medical lasers have been evolving since Theodore Maiman introduced the first ruby laser in 19601. Beyond tissue coagulation and ablation, the largest contribution advancing the understanding of tissue interaction came when Anderson and Parrish published their study of selective photothermolysis in Science in 19832. The theory taught that lasers can target selective chromophores in tissue when taking into consideration the laser wavelength, the pulse duration, and the thermal relaxation time of the target which is dependent on its size and dimension. The end goal of laser therapy is to affect the target in some desired way while sparing nearby surrounding tissues. Desired laser tissue effects can include as examples denaturation, coagulation, apoptosis and necrosis.
Since Maiman, there have been many advances in laser technology including the introduction of new wavelengths, increased laser fluences, longer and shorter pulse durations and the evolution of increasing spot sizes. One example of this evolution is the GentleMax Pro, a laser system designed and manufactured by Candela Corporation.
This paper will discuss a wide variety of applications of the GentleMax Pro, a dual wavelength platform emitting 755nm laser energy from an alexandrite laser and 1064nm laser energy from a Nd:YAG laser. Both wavelengths have reasonably good transmission in skin, with 1064 nm being less sensitive to melanin and more sensitive to oxyhemoglobin compared to 755 nm (Figure 1).
These wavelengths have been well studied for the removal of unwanted hair. They have also been used to treat both vascular and pigmented lesions. In addition, the Nd:YAG laser has been utilized to rejuvenate aging skin3, to treat hyperhidrosis4, and onychomycosis5. Melanin is the primary target for hair and pigmented lesion applications while hemoglobin is the primary target for vascular applications.
The GentleMAX Pro™ incorporates a Dynamic Cooling Device™ (DCD) that applies bursts of cooling cryogen in adjustable spray durations before and after the laser pulse. The DCD assists with the protection of the epidermis which reduces the risk of scarring and pigmentation changes such as post-inflammatory hyperpigmentation (PIH).
Hair Removal Treatments
The desire for hair removal has been around for thousands of years and date back as far as the Egyptians who were reported to have used depilatory creams. The 1800’s introduced the razor and galvanic electrology, and lasers were first described as a method to remove hair in 1963 by Leon Goldman6 but this technique did not reach commercial +use until the 1990’s.
In order to understand how lasers are used to remove hair, we must first discuss anatomy and biology of the hair follicle and the cycle of hair growth7. The important structures are the dermal papilla, hair shaft, the blood vessels and the bulge area. Cells from both the dermal papilla area and the bulge area may generate hairs, thus in order to destroy the hair, both areas must be damaged. The theory of selective photothermolysis predicts that laser light in the wavelengths from 690 nm to 1064 nm can be preferentially absorbed by the pigment in the hair shaft and by pigmented cells in the dermal papilla to damage or destroy the hair8. (See Figure 1) The longer millisecond pulse durations used in hair removal will allow the pigment in the hair shaft and dermal papilla to dissipate the heat so that the laser energy is able to destroy the desired target which is the hair follicle.
Understanding the cycle of hair growth is also an important factor in laser hair removal. The four cycles of hair growth are anagen, catagen, telogen and exogen. Anagen is the active growth phase of the hair. In this phase, melanin synthesis and growth of the hair shaft begins and towards the end of this phase there is the highest amount of melanin in the hair follicle and the deepest penetration of the hair into the skin. The catagen phase is the resting phase where growth of the hair and melanin production stops. In the telogen phase, the hair begins to lose its attachment to the dermal papilla and shrinks in size. At the end of the telogen phase, the hair eventually falls out of the hair follicle, and the follicle enters the exogen phase. The hairless follicle remains dormant until the start of a new anagen growth phase. The hair is most susceptible to laser light energy during the early to mid anagen phase where the hair follicle has generated a good amount of melanin but before the hair follicle has a chance to extend deep into the dermis9,10.
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