Laser Surgery in Dark Skin

Tina S. Alster, MD, Elizabeth L. Tanzi, MD

Disclosures
In This Article

Pigment-Specific Lasers

Pigment-specific laser technology generates green, red, or near-infrared light to selectively target intracellular melanosomes or tattoo pigment. Pigment-specific lasers are also used to eradicate unwanted hair by damaging follicular structures in which melanin is heavily concentrated.

Q-switched systems generating nanosecond (ns) pulses, which are substantially shorter than the 10-100 ns thermal relaxation time of melanosomes, represent the safest means for treating pigmented lesions in dark skin. Q-switched systems currently available include the 532 nm frequency-doubled Nd:YAG, 694 nm ruby, 755 nm alexandrite, and 1064 nm Nd:YAG lasers. Although melanin absorbs energy throughout this range of wavelengths, its absorption peaks lie in the ultraviolet range, with decreased absorption capacity at the longest wavelengths. Thus, the far infrared wavelengths generated by the alexandrite and Nd:YAG laser systems are less efficiently absorbed by epidermal melanin, which limits the extent of unwanted thermal injury to nontargeted tissues of the epidermis and upper papillary dermis. This, in turn, allows for deeper dermal penetration, making the effective treatment of pigmented dermal lesions and hair follicles possible. Whether targeting superficial epidermal lesions such as lentigines, ephelides, café-au-lait macules, or lesions with a deep dermal component such as nevus of Ota, melanocytic nevi, or nevus spilus, treatment should be initiated at threshold fluences (the minimum fluence necessary to produce immediate lesional whitening signaling the destruction of intracellular melanosomes). If the clinical threshold is exceeded, epidermal exfoliation and pinpoint bleeding ensues, resulting in blistering, possible temporary or permanent hypopigmentation, and perhaps even skin textural changes or scarring.[8,10]

Of the pigmented lesions that disproportionately affect ethnic groups with darker phototypes, nevi of Ota have proved especially amenable to treatment with Q-switched ruby, alexandrite, and Nd:YAG lasers.[11,12,13] Of these systems, the alexandrite laser appears to offer distinct advantages over other modalities as its longer wavelength produces less epidermal damage than does the ruby laser and, since it requires lower fluences than does the Nd:YAG, less tissue splatter is produced intraoperatively.[13] (Figures 1 A & B)

Nevus of Ota in a patient with type III/IV skin

Clearing noted after five Q-switched 755 nm alexandrite laser treatments

Because multiple different pigments may be present in a tattoo, effective treatment can require the use of wavelengths throughout the visible and near-infrared spectrum. Tattoos may respond unpredictably to laser treatment not only because their chemical compositions are highly variable, but also because they can be placed in the deep dermis. Treatment is more difficult and unpredictable in patients with darker skin phototypes because of the presence of significant amounts of epidermal melanin that absorbs the laser energy. As described previously, systems that generate energy characterized by longer wavelengths cause less collateral epidermal damage and penetrate more deeply, affording a safer and usually more effective form of treatment. Although the Q-switched 694 nm ruby laser is highly efficacious in removing black and blue tattoo pigments, its wavelength is strongly absorbed by epidermal melanin and its potential for inducing long-term dyspigmentation or other untoward side effects is relatively high in patients with darker skin tones. Thus, the Q-switched Nd:YAG (1064 nm) or alexandrite (755 nm) laser would be a better choice for treating blue and black tattoo pigments in darker skin since its energy is less well absorbed by epidermal melanin. Epidermal ablation with a resurfacing laser may enhance the safety and effectiveness of tattoo removal in patients with darker phototypes by eliminating the problem of competitive melanin absorption.[14]

The combination of longer wavelengths, active epidermal cooling, and longer pulse durations provided by the most advanced laser technology has decreased the side effects following laser-assisted hair removal in patients with darker skin tones.[15,16,17,18,19,20,21,22,23] Several pigment-specific laser systems with relatively long (millisecond) pulse durations have demonstrated safety and efficacy in darker skin phototypes, including the 755 nm alexandrite,[17,18,19] 810 nm diode,[20,21] and 1064 nm Nd:YAG.[23,24] Intense pulsed-light treatment of hirsutism in patients with darker skin phototypes may also be possible; however, studies have been limited.[22] One study[24] demonstrated significant long-term hair reduction after a series of 3 monthly long-pulsed 1064 Nd:YAG laser treatments in 20 women with skin phototypes IV-VI. (Figures 2 A & B) Adverse effects were limited to transient pigmentary alteration without fibrosis or scarring.[24] Pseudofolliculitis barbae, a condition with a high incidence in the African American population, has also been shown to respond favorably to laser-assisted hair removal with minimal untoward sequelae.[20,21]

Dark terminal hair on the chin in a patient with type V skin

Reduced hair seen 6 months after third long-pulsed 1064 nm Nd:YAG laser treatment

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