November 15, 2011

In the November issue of Journal of Drugs in Dermatology (2011;10:1235-9), Dr. Eliot F. Battle Jr., gives an excellent review of "Advances in Laser Hair Removal in Skin of Color."

Dr. Battle summarizes that "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."

The mechanism of laser hair reduction (LHR) is based on the theory of selective photothermolysis, whereby thermal injury to a desired chromophore can be achieved with the appropriate wavelength, pulse duration, and fluence.

In LHR, the target chromophore is the pigment in the hair follicle and bulb. However, Dr. Battle notes that destruction of the non-pigmented progenitor stem cells is also required to achieve permanent hair reduction. Therefore, a modified theory of selective photothermolysis has been proposed for the mechanism of LHR where appropriate wavelengths, as well as longer pulse durations, must be used to allow heat to effectively destroy the melanocytic hair follicle and bulb, as well as the amelanotic hair follicle and stem cell. 

In darker skin types, longer wavelength lasers must be used to bypass absorption of epidermal pigment to prevent untoward side effects of dyspigmentation.

Currently the 810-nm diode and 1064-nm Nd:YAG lasers are Food and Drug Administration approved for skin types IV-VI. The Nd:YAG is inherently the safer of the two devices because of the longer wavelength; however,  long pulse durations with the diode laser with appropriate cooling have been shown to increase its safety profile.

Epidermal damage from lasers occurs when the epidermal temperature equals or exceeds 45 degrees Celsius, thus appropriate cooling mechanisms are essential for safe and effective LHR. Excessive cooling, however, can lead to dyspigmentation in darker skin.

Initiating LHR in darker skin should be done conservatively with longer wavelengths, lower fluences, and longer pulse durations. If test spots are performed, it is recommended to wait 48 hours before proceeding with therapy as patients with darker skin may manifest delayed dyspigmentation.

Patients with skin types IV-VI may also be at increased risk for paradoxical hypertrichosis. While it has been reported in most ethnic origins, those of Mediterranean and Pacific Asian descent may be particularly affected. Paradoxical hypertrichosis mainly occurs on the face and neck, and has been reported both within and outside the treatment area. While the exact cause is unknown, possible causes include the effect of inflammatory mediators and subtherapeutic thermal injury causing induction of the hair cycle. Current treatment for paradoxical hypertrichosis is laser therapy of the affected area.

The only contraindications for LHR are gold therapy and St. John’s Wort, which should be discontinued for 3 months prior to therapy. While not contraindicated, LHR is not recommended in pregnant women. 

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