Laser hair removal is a relatively new method of removing unwanted hair. It is faster and less painful than electrolysis (uses electric current to damage hair follicles) but more expensive. Multiple treatments can permanently eliminate some hairs and delay the growth of others. It is particularly useful for treating excessive hair growth conditions (e.g., hirsutism, hypertrichosis) but may be used to eliminate nearly any unwanted hair.

Human hairs may be either terminal (darkly pigmented, coarse and long) or vellus (lightly pigmented, fine and short). Laser hair removal typically targets terminal hairs. Both forms share the same anatomy. The lowermost part of the hair follicle is the bulb. Located in the dermis, this bulb is responsible for the formation of the hair. Damage to the bulb may make it unable to produce hair, resulting in permanent hair loss.

Hair growth occurs in cycles, including an active growing cycle (anagen) and a dormant cycle in which the hair does not grow (telogen). It is only in the active growing cycle that the bulb can be damaged to make it incapable of producing hair.

Because hair growth cycles are staggered throughout the body (some hair is in anagen while some is in telogen), multiple laser treatments are necessary to produce maximum permanent hair reduction.

During laser hair removal, laser light energy passes through the skin and targets the pigment melanin in the hair follicles. Melanin absorbs the energy and the hair follicle is heated and destroyed without harming the skin and surrounding tissue. This temporarily halts hair growth and permanently reduces, thins and lightens hair in the treatment area.

Some individuals experience long-term hair removal which lasts for several years. Others will require regular treatments every one to three months to maintain the hair loss. The degree of permanent hair reduction depends on several factors, including the color and coarseness of the patient's hair, and the fluence (density of light) used. Multiple treatments (usually around four) are necessary for maximum hair reduction and may be staggered by weeks or months. The highest tolerated fluence is required for optimal results and treatment responses vary among individuals. It is impossible to predict the number of treatments a peson will require or the length of time their hair will remain absent.

Generally, patients with light skin and dark hair have the best results. The treatment is more effective on light skin because there is less melanin in the skin to compete for laser energy, so the energy more effectively targets the hair follicle instead of the skin. Patients with dark skin tend to experience more side effects because of the higher levels of melanin in the skin. There are newer methods of laser treatment that can be used for patients with dark skin (e.g., Nd:YAG lasers).

Conversely, the darker the hair, the more energy is absorbed and the more effective the treatment. Individuals with light hair (e.g., blonde, red) do not respond to laser hair removal because their hair follicles lack the pigment needed for the hair to absorb the laser's energy.

Laser hair removal can be used in any area other than around the eyes. Commonly treated areas include the upper lip, chin, ears, chest, back, armpits, legs and arms. Areas of thin skin (e.g., armpits, bikini area) tend to respond better than areas of thick skin (e.g., back, chin), requiring fewer treatments.