Laser Hair Removal Pearls in Skin of Color

By Keyvan Nouri MD, Yasser Alqubaisy MD and Michael P. McLeod MS

INTRODUCTION
Laser hair removal (LHR) has been used in clinics since 1995; however, it was approximately 50 years ago that laser energy was first noted to “char” hair in the laboratory.1,2 The use of laser energy for hair removal has substantially advanced in both technology and knowledge. Today, LHR has become one of the most requested procedures in cosmetic dermatology.3

The theory behind which the laser beam is known to affect or cause a decrease in hair growth is largely based upon Anderson and Parrish’s theory of selective photothermolysis, and later, extended photothermolysis.4,5 Basically, a pulse of laser energy emitted at a particular wavelength is absorbed by a targeted chromophore and does not cause damage to nearby structures as long as the pulse duration does not extend beyond the chromophore’s thermal relaxation time.4 In the case of LHR, extending the pulse duration beyond the thermal relaxation time is beneficial; this allows the thermal energy absorbed by the hair follicle to diffuse to the stem cells in the follicular bulge region, thereby causing permanent hair reduction instead of temporary hair removal.3 The targeted chromophore in LHR is melanin within the hair follicle located approximately 2–5 mm in the dermis.6 This poses a problem in skin of color (SOC) or the darker Fitzpatrick skin types (IV–VI). A significant amount of melanin in the epidermis in SOC competes for the absorption of laser energy with the melanin in the hair follicle. When too much laser energy is absorbed by the melanin in the epidermis, as opposed to the hair follicle, complications such as permanent pigment alteration (hypopigmentation) or burns can arise.

SETTINGS AND METHODS
The ideal patient for laser hair removal has a low Fitzpatrick skin type and dark hair, thereby minimizing the competition between the melanin of the epidermis and the melanin of the hair. In order to minimize unwanted laser energy absorption by epidermal melanin in SOC (Fitzpatrick Skin Types V–VI), a wavelength should be chosen that minimizes the epidermal melanin’s absorption. The epidermal melanin absorbs less light as one progresses towards longer wavelengths in the electromagnetic spectrum. Thus, the long pulsed 1064 nm Nd:YAG is able to safely pass through the epidermal melanin while still allowing sufficient absorption of the follicular melanin to be an effective tool for LHR.

Unfortunately, the 1064 nm Nd:YAG laser is not quite as effective as the 755 nm alexandrite laser, which can be safely used in lighter skin types, because just as there is less epidermal melanin absorption, there is also less follicular melanin absorption.7 It is better to carry out more treatment sessions with the Nd:YAG laser than risk permanently altering the patient’s cutaneous pigment. The clinical endpoint when performing laser hair reduction in SOC patients with the Nd:YAG laser is perifollicular erythema and edema.3 The fluence should be adjusted to achieve this endpoint. It is best to start at lower fluences and work one’s way upwards to achieve that endpoint, especially when treating new SOC patients. Higher fluences yield more permanent hair reduction, but must be carefully used because they can result in more side effects.8,9 A lower setting on the dynamic cooling device should be used, as too high of a setting in SOC can lead to cryogen burns with post-inflammatory pigmentation (Figure 1). Longer pulse durations lead to more effective hair reduction, adhering to the hypothesis of extended photothermolysis.

FIGURE 1. Photograph of an individual treated with an excessively high dynamic cooling device setting. Note the hyperpigmented macules distributed over the medial side of the lower leg.

Certain anatomical locations respond better to LHR and similarly, other locations are associated with more side effects. Notably, areas that traditionally exhibit thinner skin, such as the axilla, have been reported to result in better hair reduction than thicker-skinned areas such as the leg or chin.6 The sun-exposed locations have been reported to exhibit more side effects such as vesiculation and temporary pigment changes.6 It should also be noted that the incidence of paradoxical hypertrichosis is also higher in darker skin types, with most reports occurring in females (Fitzpatrick skin types III–IV) with polycistic ovarian syndrome along the side of the face after treatment with IPL or the 755 nm long pulse alexandrite laser (Figure 2).10,11 The etiology behind this phenomenon remains undiscovered12; however, many investigators have suggested that laser energy delivered at too low of a fluence may actually stimulate nearby hair follicles to begin a robust phase of anagen.13,14

FIGURE 2. Photographs of a 22-year-old woman (skin type IV) a) before and b) after two treatments with a long-pulse 755 nm alexandrite laser of the chin and beard area: 18-mm spot size, energy level of 20 J/cm2, and 3 ms pulse.12 Reproduced with permission from Blackwell Publishing.

CLINICAL BOTTOM LINE
In conclusion, the competition between epidermal and follicular melanin in SOC dictates which laser wavelength should be used for achieving the optimal balance of safety and efficacy. The long pulsed 1064 nm Nd:YAG laser allows enough energy to safely pass through the heavily melaninated epidermis, while still being absorbed by the follicular melanin in sufficient quantities to reduce hair growth. The longer pulse duration allows for diffusion of the absorbed follicular energy to affect the follicular stem cells in the bulge region, thus thought to cause permanent hair reduction. Lower fluences should be used at first in new SOC patients and then gradually increased to safely achieve perifollicular erythema and edema.

DISCLOSURES
The authors have no relevant conflicts of interest to disclose.

REFERENCES
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About the author

Keyvan Nouri MD, Yasser Alqubaisy MD and Michael P. McLeod MS

Department of Dermatology and Cutaneous Surgery, University of Miami Miller School of Medicine, FL

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