A s the fourth most common non-surgical cosmetic procedure performed in the United States today, laser hair removal’s popularity has soared since its introduction nearly a decade ago.1 However, until recently, safe laser hair removal was limited in Fitzpatrick skin types I to III. Now, however, there are treatments available that have greatly improved the safety of laser hair removal in patients with skin types IV to VI. In this article, I’ll highlight the main improvements in technology that have enabled laser hair removal to be a much safer and viable option for patients who haven’t previously optimally benefited from laser hair removal. Revisiting How the Technology Works As you’re probably aware, laser hair removal works by the theory of selective photothermolysis. This theory asserts that the specific wavelength of light produced by the laser should correspond to the wavelength that is preferentially absorbed by its target or chromophore. In the case of laser hair removal, the chromophore is the melanin found in hair follicles. Additionally, the theory proposes that the thermal injury induced is limited to the target if the exposure duration (pulse width) is less than or equal to the time necessary for cooling of structures (thermal relaxation time).2 The absorption spectrum of melanin ranges from 320 nm to 1200 nm with the greatest absorption observed in the low end of this spectrum. The ruby (694 nm) was the first laser introduced for laser assisted hair removal and is highly absorbed by all melanin in the skin. This melanin absorption includes not only the targeted melanin in the hair follicle but also epidermal melanin. In darkly colored skin, epidermal absorption of energy leads to vesiculation and damage of the treated areas. This phenomenon made the ruby laser safe for only skin types I to III. Until recently, safe and effective laser hair removal was limited in patients with Fitzpatrick skin types IV to VI due to the significant epidermal melanin present in these patients. Four Important Concepts to Consider The main objective in treating patients with skin of color is to avoid epidermal melanin absorption of laser energy and resultant thermal injury. Four main concepts are important in achieving this objective: 1. Longer wavelengths are less selective for melanin. These wavelength lasers are less selective for melanin than the shorter wavelength lasers (694 nm) that were originally introduced. Thus, longer wavelength lasers avoid melanin absorption by the epidermis but are still selective enough to target the melanin in the dark, black hairs. 2. Longer wavelengths penetrate deeper into the dermis. Longer wavelength lasers theoretically bypass the epidermis to reach their target deep at the bulb or the bulge of the hair follicle. Thus, not only are the long wavelengths less selective for epidermal melanin, they also penetrate deeper to further diminish the risk of epidermal damage. 3. Longer pulse widths are essential for achieving safe laser hair removal. The first lasers introduced for hair removal had short pulse widths ranging from 3 ms to 10 ms. However, even with the ruby laser, early investigations demonstrated that longer pulse widths improved safety.3 To understand why this is true, you must refer to the original theory of selective photothermolysis. Based on this theory, the pulse width must be less than the “cooling time” of the target to cause thermal injury. For the epidermis, the “cooling time” is approximately 3 ms to 10 ms. Ideally, to avoid thermal injury to the epidermis, a pulse duration of longer than 10 ms would allow sufficient cooling of the epidermis. In other words, by delivering energy over a longer period of time, the basal layer is allowed to cool as it’s heated.4 To achieve follicular damage, however, the pulse duration should be less than the cooling time of the follicle, which is estimated at 40 ms to 100 ms. Combining these concepts, the ideal pulse duration for laser hair removal is greater than 10 ms (to spare the epidermis) but less than 100 ms (to target the hair follicle). In skin types V and VI, pulse widths of 30 ms or more are most frequently used. 4. Appropriate cooling is the final requirement that is essential in treating skin of color. With appropriate pre and post cooling of skin, side effects can be minimized. Most laser devices, with the exception of the original ruby laser, utilize some form of cooling when treating patients. Both cryogen spray and contact cooling have been studied and can achieve epidermal temperatures of –5 degrees to 5 degrees Celcius.5 Additionally, post cooling with ice packs after laser treatments can be helpful not only for patient comfort, but also to improve epidermal cooling after laser treatments. Studies with Alexandrite and Diode Lasers Given these four important concepts, the original ruby laser with its short wavelength, short pulse width, and lack of cooling made safe treatment of Fitzpatrick skin types IV to VI virtually impossible. The alexandrite (755 nm) and the diode (800 nm to 1000 nm) were later introduced for laser hair removal. These lasers have longer wavelengths allowing for a larger variety of patients to be treated. Here’s a look at some of the outcomes of the studies with these lasers and another promising laser technology for hair removal in darker skin types. • In one study, a long-pulsed 755 nm laser with a 40 ms pulse width was used to treat 150 patients with skin types IV to VI. A test site with a fluence of 16 J/cm2 was first performed and energy fluence was selected according to response. The authors reported an overall complication rate of 2.7%; however, only two patients with skin type VI were included in the study and both developed blistering.6 • A smaller study of the alexandrite (755 nm, 3 ms pulse width) included four women with Fitzpatrick skin type VI. In this study, lower fluences were used (8 J/cm2 to 14 J/cm2), and no side effects were noted.7 Although treatment of skin types IV to VI is possible with the alexandrite, the associated risk is still great in these patients. • The diode laser has been studied with greater success in the treatment of darker-skinned patients. The 800 nm diode laser was studied with pulse widths of 30 ms and 100 ms. The authors reported that although both settings could be used safely, longer pulse widths (100 ms) allowed higher fluences to be utilized with less complications.8 • Another study utilized the 810 nm diode laser to treat eight patients with skin types V and VI. These patients were treated with low fluence of 10 J/cm2 and a pulse width of 30 ms. Transient blistering and pigment alterations were noted in some patients despite the lower fluence utilized.9 Based on these studies, the diode laser offered increased safety of laser hair removal in African-American patients, however, complications remained an issue. Safer, More Effective Technology Most recently, the Nd:YAG (1064 nm) laser was introduced which provides safe laser hair removal in all skin types including the darker skin types of African-American patients. In one study, 20 patients with skin types IV through VI were treated with a series of three laser sessions. The pulse width utilized was 50 ms, the fluence ranged from 40 J/cm2 to 50 J/cm2, and a contact sapphire tip cooling device was used. Adverse events from all 60 treatments included transient pigment alteration (5%) and rare vesiculation (1.5%).10 In another study 37 patients with pseudofolliculitis barbae were treated with the long-pulsed Nd:YAG. The authors concluded that the long-pulsed Nd:YAG offered a safe and effective treatment for patients with pseudofolliculitis barbae.11 In summary, with the introduction of the long-pulsed Nd:YAG laser, patients with skin types V and VI can finally enjoy the benefits of laser hair removal with minimal risk of side effects. These lasers provide permanent hair reduction in patients with unwanted body hair. Additionally, they offer new and effective treatment options for African-American women with hirsutism and patients with pseudofolliculitis barbae.