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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.
Hair removal lasers have been in use since 1997 and have been approved for "permanent hair reduction" in the United States by the Food and Drug Administration (FDA). Under the FDA's definition, "permanent" hair reduction is the long-term, stable reduction in the number of hairs regrowing after a treatment regime. Indeed, many patients experience complete regrowth of hair on their treated areas in the years following their last treatment. This means that although laser treatments with these devices will permanently reduce the total number of body hairs, they will not result in a permanent removal of all hair.
Laser hair removal has become popular because of its speed and efficiency, although some of the efficacy is dependent upon the skill and experience of the laser operator,and the choice and availability of different laser technologies used for the procedure. Some will need touch-up treatments, especially on large areas, after the initial set of 3-8 treatments. It has also been noted that some people are "non-responders" – this occurs when incorrect device is being used, the device parameters are too low or the patient is simply not a good candidate for treatment.
Number of 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.
Side Effects and Risks of Laser Hair Removal Treatments
Some normal side effects may occur after laser hair removal treatments, including itching, redness, and swelling around the treatment area. These side effects rarely last more than three days. The most common serious side effect is change in skin pigment.
Some level of pain should also be expected during treatments. Numbing creams are available at most clinics, sometimes for an additional cost. Some numbing creams are available over the counter. Use of strong numbing creams over large skin areas being treated at one time must be avoided, as this has seriously harmed, and even killed, patients.Typically, the cream should be applied about 30 minutes before the procedure. Icing the area after the treatment helps relieve the side effects faster.
Unwanted side effects such as hypo- or hyper-pigmentation or, in extreme cases, burning of the skin call for an adjustment in laser selection or settings. Risks include the chance of burning the skin or discoloration of the skin, hypopigmentation (white spots), flare of acne, swelling around the hair follicle, scab formation, purpura, and infection. These risks can be reduced by treatment with an appropriate laser type used at appropriate settings for the individual's skin type and treatment area.
Some patients may show side effects from an allergy to either the hair removal gel used with certain laser types or to a numbing cream.
Rare side effects include blistering, scarring and skin texture changes.