• #9. Development of Hair Removal Lasers I


    Ablative lasers have been developed by the sporadic efforts of many people, and these efforts are still continuing. As described in the previous article, the development process of ablative lasers for wrinkle, scar and elasticity enhancement was drastically accelerated by the advent of Cooltouch, leading to the development of various lasers with less downtime in daily life. However, these lasers had substantially low efficacy and therefore were not successful in the market. Instead, the market favored RF devices with similar concept and theory or fractional photothermolysis lasers because these devices made moderate downtime in daily life. With the introduction of new devices that have similar effect as lasers, both doctors and patients began to recognize the possibility of improving wrinkles, enhancing skin elasticity and treating scars without surgery using these devices, leading to a gradual expansion of the market. Among the devices other than laser, ultrasound, has also added to the variety of choices made available to the consumers in this market.


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         This article first addresses the development of hair removal lasers, before discussing the development of lasers and medical devices for wrinkle and scar in the 2000s. Laser hair removal was introduced in the mid-1990s and now is one of the most common aesthetic procedures. Due to a recent decline in the cost of laser hair removal and simplicity of the procedure, operators other than doctors are carrying out the procedures. Thus, medical institutions and doctors are losing interest in laser hair removal. However, hair removal was the newest and most important aesthetic laser therapy in the western countries between the 1990s and early 2000s.
        The possibility of hair removal with laser was first observed in the 1960s by Leon Goldman who detected skin change after laser irradiation, but the actual device was developed and released in the market only 17 years ago.
        One cannot discuss the development of hair removal laser without mentioning the early ruby laser (Epilaser. Palomar). In the early 1990s, when lasers for selective photothermolysis, including dye laser for vascular treatment and Q-switched ruby, alexandrite and Nd:YAG lasers for the treatment of tattoo and pigmentation were widely used in clinical practice, Dr. Rox Anderson was interested in developing a new laser using his own theory. He successfully developed a hair removal laser using the Selective Photothermolysis theory in the mid-1990s. As mentioned in the previous article, a new therapeutic laser can be developed under the following three conditions; the efficacy is markedly increased despite low demand; the efficacy is moderately increased with moderate demand; or the efficacy is slightly increased but the potential demand is very high. Laser hair removal was developed for a moderate demand.


    History of Lasers for Hair Removal

        The history of medical hair removal started with electrolysis in the western countries. In 1875 an ophthalmologist named Charles Michael in St. Louis, US, developed electrolysis for the treatment of trichiasis. This technique later evolved into a hair removal procedure and a lot of electrologists opened hair removal clinics in major cities in the US, Canada and Europe in the 1990s. They were not doctors or nurses but authorized experts who had to receive a certain period of education and pass the government test.
        The electrolysis was also very common in major cities of Japan. Dr. Kobayashi developed Kobayashi insulated needles to reduce skin irritation, which were also introduced in Korea. Some hospitals in Korea trained their staff to conduct electrolysis and university hospitals sporadically had specialists conduct electrolysis, however, electrolysis for hair removal was far from becoming popular and the demand was limited. I also have experienced a case of electrolysis 4-5 hours a day for a week in the early 1990s during my dermatology residency program. As there was a strong demand for hair removal procedures in the West, it was only a matter of time before a technique more effective and simpler than electrolysis could be widespread.
        Electrolysis is a time-consuming procedure (a study reported a 13 times longer treatment time than laser hair removal), has a high likelihood of side effects and is very painful. Furthermore, electrolysis does not always guarantee satisfying outcome because the procedure requires inserting a fine electric needle to the hair follicle to an appropriate depth, yielding variable outcomes depending on the skill of the electrologist.
        In contrast, the advantages of the laser hair removal in the 1990s were summerised as 1. not painful, 2. Short treatment time, and 3. less side effects. However, these advantages of laser relative to electrolysis were not compelling enough as the number of patients who had experienced the electrolysis before laser hair removal drastically declined in the 2000s.
        Dr. Rox Anderson and his team in the Wellman Center of Harvard medical School conducted an animal test and clinical study using a ruby laser (694nm) that is relatively well absorbed by melanin in the hair shaft. Because a human hair shaft can be assumed as a cylinder composed of melanin, tens to 100um in diameter, the thermal relaxation time was calculated and used a normal mode ruby laser with a pulse duration in ms domain (the first test actually used 270us, 6mm spot size). The animal test used ex vivo blackhaired dog skin (Grossman MC, Dierickx C, Farinelli W, Flotte T, Anderson RR. Damage to hair follicles by normal-mode Ruby Laser pulses. J Am Acad Dermatol. 1996 Dec;35(6):889~94) and the preliminary teat hair removal treatments were done to the  staffs of the Wellman Center, including Dr. Rox Anderson himself. The results were published in a paper (Dierickx CC, Grossman MC, Farinelli WA, Anderson RR. Permanent hair removal by normal-mode Ruby Laser. Arch Dermatol. 1998 Jul;134(7):837~42). In the early 1990s when lasers for hair removal were being developed, Dr. Cotsarelis, a professor of dermatology at University of Pennsylvania, reported bulge hypothesis regarding hair stem cell (Cotsarelis G, Sun TT, Lavker RM. Label-retaining cells reside in the bulge area of pilosebaceous unit: implications for follicular stem cells, hair cycle, and skin carcinogenesis. Cell. 1990 Jun 29;61(7):1329~37). However, this was before the development of stem cell staining in the tissue of human hair by the same investigators (Lyle S, Christofidou-Solomidou M, Liu Y, Elder DE, Albelda S, Cotsarelis G. The C8/144B monoclonal antibody recognizes cytokeratin 15 and defines the location of human hair follicle stem cells.J Cell Sci. 1998 Nov;111 (Pt 21):3179~88).
        Thus, the location of hair stem cell was not considered for understanding the mechanism of action of hair removal laser and the device was developed based on the hair shaft data alone, and was evaluated for the efficacy of actual hair removal. For these reasons, Dr. Rox Anderson and the investigators conducted the test with ruby laser, which was easily accessible in his laboratory at the time, adding a skin cooling system to protect the skin surface and increasing the pulse duration to 3ms. This laser for hair removal was introduced at the 1996 American Academy of Dermatology, becoming the first laser for hair removal (Fig. 1. Epilaser. Palomar medical technologies).


    Fig 1. Epilaser.


        I joined the Wellman Center in 1998, when they started to turn their attention to various other lasers for hair removal. I naturally participated in a study in these endeavors. At the time, Dr. Rox Anderson and I both suspected that damaging the hair stem cell or papilla cell would be an ideal mechanism for hair removal, without knowing the exact location of the hair stem cell. Fig. 2 shows the histological image of a stained stem cell I found at the cross-section of a human hair after attending a lecture by Dr. Cotsarelis before the publication of his paper in 1998. The image clearly shows that the hair stem cell is located quite far from the hair shaft. This finding indicates that the chromophore that absorbs the laser energy is located far from the target cell and additional time is needed for the heat energy created in the hair shaft to reach the hair stem cell, suggesting that the pulse duration should exceed 3ms for the laser to be more effective.


     Fig 2. CD8/144B (hair stem cell) staining. Brown stained stem cell is located at the outermost layer of the outer root sheath, with a considerable distance from the hair shaft.


    From the late 1990s, laser manufacturers started to release various kinds of lasers for hair removal with similar mechanisms to Epilaser, the first hair removal laser, but with completely different specifications. After the development of Epilaser (Palomar), alexandrite lasers, including Gentlase (Candela) and Apogee (Cynosure), and  LightSheer ( a long pulse diode laser developed by Star Medical, a subsidiary company of Palomar, and marketed by Palomar, by Coherent after then, and currently by Lumenis) were released. From the 2000s, the Extended Theory of Selective Photothermolysis and Thermal Damage Time were introduced for understanding the mechanism of laser hair removal (Altshuler GB, Anderson RR, Manstein D, Zenzie HH, Smirnov MZ. Extended Theory of Selective Photothermolysis. Lasers Surg Med. 2001;29(5):416-32).


    -To be continued-


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