The efficacy of laser hair removal is now generally accepted in dermatology and laser hair removal is widely practiced in clinics, and specially designed devices are available for self-treatment at home.
Mechanism of action
The primary principle behind laser hair removal is selective photothermolysis (SPTL), the matching of a specific wavelength of light and pulse duration to obtain optimal effect on a targeted tissue with minimal effect on surrounding tissue.
Lasers can cause localized damage by selectively heating dark target matter, melanin, in the area that causes hair growth, the follicle, while not heating the rest of the skin. Light is absorbed by dark objects, so laser energy can be absorbed by dark material in the skin, but with much more speed and intensity. This dark target matter, or chromophore, can be naturally-occurring or artificially introduced.
Melanin is considered the primary chromophore for all hair removal lasers currently on the market. Melanin occurs naturally in the skin, and gives skin and hair their color. There are two types of melanin in hair. Eumelanin gives hair brown or black color, while pheomelanin gives hair blonde or red color. Because of the selective absorption of photons of laser light, only black or brown hair can be removed. Laser works best with dark coarse hair. Light skin and dark hair are an ideal combination, being most effective and producing the best results, but new lasers are now able to target dark black hair with some success in patients with dark skin.
Laser treatment sessions
Multiple treatments depending on the type of hair and skin color have been shown to provide long-term reduction of hair. Most patients need a minimum of seven treatments. Current parameters differ from device to device but manufacturers and clinicians generally recommend waiting from three to eight weeks depending on the area being treated. The number of sessions depends on various parameters, including the area of the body being treated, skin color, coarseness of hair, reason for hirsutism, and gender. Coarse dark hair on light skin is easiest to treat. Certain areas (notably men’s faces) may require considerably more treatments to achieve desired results. Hair grows in several phases (anagen, telogen, catagen) and a laser can only affect the currently active growing hair follicles (anagen).Hence, several sessions are needed to kill hair in all phases of growth. This problem is countered by spacing appointments sufficiently so that inactive follicles will start to grow again.
Laser does not work well on light-colored hair, red hair, grey hair, white hair, as well as fine hair of any color, such as vellus. For darker skin patients with black hair, the long-pulsed Nd:YAG laser with a cooling tip can be safe and effective when used by an experienced practitioner.
Intervals between sessions
Usually treatments are spaced three to eight weeks apart depending on the body area and the hair cycle length for that area. The face usually requires more frequent treatments three to four weeks apart, whereas legs require less frequent treatments and patients should be advised to wait at least six weeks.
Typically the shedding of the treated hairs takes about two to three weeks. These hairs should be allowed to fall out on their own and should not be manipulated by the patient.
Hair removal lasers are effective treatment for pseudofolliculitis barbae, commonly called “ingrown hairs” or “shaving bumps”. They have recently been reported as helpful treatment for pilonidal cysts, since they eliminate the ingrown hairs that produce the troublesome foreign body reactions in this congenital malady.