Advances in Laser Hair Removal in Skin of Color
November 2011 | Volume 10 | Issue 11 | Original Article | 1235 | Copyright © 2011
Eliot F. Battle Jr. MD
Cultura Cosmetic Dermatology and Laser Center, Washington, DC
Laser hair removal, previously contraindicated in patients with ethnically dark (phototypes IV-VI) or sun-tanned skin, is now recognized as a safe and effective method of permanent hair reduction in all patients. Longer wavelengths, conservative fluences, longer pulse durations and appropriate cooling methods are necessary to minimize untoward side effects and maximize efficacy. The longer wavelength Nd:YAG laser is considered safest in treating darker skin of color. An added benefit of laser epilation is that side effects of conventional hair removal such as pseudo-folliculitis barbae and post inflammatory dyspigmentation, more commonly seen in skin of color, may also respond favorably to the laser, thus increasing the potential for patient satisfaction.
J Drugs Dermatol. 2011;10(11):1235-1239.
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The removal of unwanted hair, an accepted practice in many cultures, has been performed since ancient times. It has evolved from temporary modes of depilation (removing hair visible above the skin) and epilation (removal of the entire hair) such as abrasion, chemical depilatories, shaving, waxing, tweezing, "sugaring," and threading, to procedures which provide more permanent hair reduction. Although permanent epilation became possible with the advent of electrolysis, this procedure proved to be, like some of the traditional methods noted above, tedious and time consuming; additionally, in those with curlier hair and darker skin phototypes (IV–VI), electrolysis was a difficult procedure, prone to result in exacerbation of inflammation, pseudo-folliculitis barbae, post-inflammatory hyperpigmentation, and scarring. Laser hair removal (LHR) revolutionized the field of epilation, providing a more cosmetically scrupulous, time-saving alternative to the hair-by-hair approach of electrolysis and the traditional methods of hair removal. Initially contraindicated in patients with ethnically dark or sun-tanned skin, LHR was recommended only for non-tanned, phototype I–III skin because of the risk of untoward side effects and worsening of pre-existing conditions more often seen in phototype IV–VI skin.
Mechanisms of Epilation in LHR in Skin of ColorThe theory of selective photothermolysis forms the foundation of cosmetic, light-based laser therapy. This theory states that thermal injury can be limited to the absorbing chromophore by using the appropriate wavelength, pulse duration, and fluence (energy density expressed as J/cm²), thereby protecting the surrounding tissue.1 In LHR, the target chromophore is the melanin-rich hair shaft and bulb, but to ensure effective results, thermal injury must also include the surrounding hair follicle. Finally, destruction of progenitor stem cells is required to permanently inhibit hair growth. In order to achieve effective results with LHR and to assure confinement of thermal damage to the hair follicle, the pulse duration should be less than or equal to the thermal relaxation time of the hair shaft, estimated to be in the range of 10–100 milliseconds.2
A "unifying" hypothesis has identified two stem cell reservoirs in the human anagen hair follicle: a distal outer root sheath reservoir and a proximal outer root sheath reservoir containing amelanotic stem cells, which may act as a melanocytic reservoir.3 In the mouse model, these stem cells are identified within the bulge,4 in the human hair follicle, the bulge is thought to reside in the lower third of the follicle of the outer root sheath.
Therefore, a modified theory of selective photothermolysis is used to describe the mechanism of LHR because the melanocytic chromophore target as well as the amelanotic (hair follicle and stem cell) target must both be destroyed to accomplish permanent hair reduction. To achieve this goal, longer pulse durations are used, allowing heat propagation to the entire hair follicle.