Laser hair removal: practice and science

March 1, 2005

Active cooling helps minimize epidermal injury — a critical factor when treating patients with darker skin phototypes.

New Orleans - Consumers spend billions each year on laser-assisted hair removal - the safest, most effective way to remove unwanted hair, according to Elizabeth Tanzi, M.D.

As co-director of the Washington Institute of Dermatologic Laser Surgery in Washington D.C., Dr. Tanzi has performed more than 2,500 hair removal procedures over the past four years. She notes two recent advances: improvement in techniques for treating people with darker skin tones; and development of faster, more powerful intense pulsed light (IPL) and laser devices that incorporate skin cooling features (ice, refrigerated gels, cryogenic sprays or contact cooling mechanisms).

Best results "My technique depends on skin type and hair thickness," she says, "but I generally advise patients they will need treatment once a month for three to five months, depending on where they want hair removal."

She adds, "The underarms and bikini line respond better than the face."

During the initial consultation, it's important to make sure patients don't have a hormone imbalance. Symptoms include weight gain, acne and hair growth in the beard and chest areas.

"This is a major reason for hair growth in undesirable areas. If the condition goes unchecked, it makes hair removal very difficult," Dr. Tanzi says.

Patients with lighter hair and skin tones (Fitzpatrick I to III) are ideal candidates, achieving 50 percent to 75 percent hair reduction, albeit with some regrowth at six months. On these patients, Dr. Tanzi uses a long-pulse alexandrite laser. For individuals with darker skin tones (Fitzpatrick IV to VI), she achieves best results with a long-pulse Nd:YAG. Pretreatment involves a numbing cream, and post-treatment uses a mild anti-inflammatory cream.

"Patients may have some redness for a few hours, but the side effects have declined dramatically."

A maintenance treatment is required every three to six months. For best results, patients should not wax or pluck prior to a laser-assisted hair removal treatment.

Mechanism of action Both wavelength and pulse duration are important for effective photoepilation. Photothermal laser-tissue interactions in the hair shaft and melanin-rich matrix heat the surrounding follicle. To limit thermal injury, scientists originally determined that the pulse duration should be less than or equal to the thermal relaxation time of the hair follicle (10 ms to 100 ms, depending upon the diameter of the follicle).

Most systems now in use were designed accordingly. However, because some components of the follicular unit, such as stem cells, do not have significant amounts of melanin and may be distant from targeted pigmented areas, researchers are now beginning to suggest longer pulse durations that will induce thermal injury throughout the follicular unit and, hopefully, lead to permanent hair reduction.

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