Epilation performed by laser was performed experimentally for about 20 years before it became commercially available in the mid 1990s. Intense Pulsed Light (IPL) epilators, though technically not a laser, use xenon flash lamps that emit full spectrum light. Laser and light-based methods, sometimes called phototricholysis or photoepilation, are now most commonly referred to collectively as "laser hair removal". One of the first published articles describing laser hair removal was authored by the group at Massachusetts General Hospital in 1998.^[1][2]

The efficacy of laser hair removal is now generally accepted in the dermatology community, and laser hair removal is widely practiced. Many reviews of laser hair removal methods, safety, and efficacy have been published in the dermatology literature.

Mechanism of action

The primary principle behind laser hair removal is selective photothermolysis. Lasers can cause localized damage by selectively heating dark target matter in the area that causes hair growth 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.

Hair removal lasers selectively target Melanin:

• Melanin is considered the primary chromophore for all hair removal lasers currently on the market. Melanin occurs naturally in the skin (it gives skin and hair its color). There are two types of melanin in hair: eumelanin (which gives hair brown or black color) and pheomelanin (which gives hair blonde or red color). Because of the selective absorption of photons of laser light, only black or brown hair can be removed.

Both men and women seek laser hair removal services to have superfluous or unwanted hair removed. Hair removal is commonly done on lip, chin, ear lobe, shoulders, back, underarm, abdomen, buttocks, pubic area, bikini lines, thighs, face, neck, chest, arms, legs, hands, and toes.

Laser is attracted to dark pigment and therefore works best with dark coarse hair. Light skin and dark hair are an ideal combination, but new lasers are now able to target dark black hair even in patients with dark skin.

Hair removal lasers have been in use since 1997 and the Food and Drug Administration approved it for “permanent hair reduction.” Laser hair removal has become extremely popular because of its speed and efficacy, although some of the efficacy is dependent upon the skill and experience of the laser operator, and the choice and availability of different laser technology at the clinic which is performing the procedure. Some will need touch-up treatments, especially on large areas, after the initial set of 3-8 treatments. It has also been observed that some people seem to be non-responders – this is not confirmed and reasons are not known, and may in fact be due to lack of skill on the part of many laser operators and/or the type of machine and settings they are using. Keep in mind that it's hard to judge whether someone’s lack of results is due to a potential underlying medical condition that causes continuous growth and makes it seem like laser isn’t working, if the treatment wasn't performed properly, or whether for some people it just doesn't work for currently unknown reasons. In essence, you can’t determine what your personal results would be like unless you try it. Results depend on many variables involved, including the tech's experience, type of laser used, how settings are set, etc. It is recommended to start with one area and see how your hair reacts before committing to a set of treatments on many areas at once.

Electrolysis is an alternative permanent hair removal method that has been used for over 135 years.^{[citation needed]} It involves treating one hair at a time and is an option for smaller areas (like eyebrows or upper lip) where precision is necessary, although even in these areas it has fallen out of favor because of the possibility of scarring and the pain of the procedure (unlike laser hair removal, local injection anesthesia is often required in order for patients to tolerate electrolysis). In addition it takes so many treatments compared to laser to complete a large area, and the extreme cost and discomfort are such that electrolysis is rarely used for large areas. At this time, it is the only permanent option for very fine and light-colored hair.

Laser parameters that affect results

Several wavelengths of laser energy have been used for hair removal, from visible light to near-infrared radiation. These lasers are usually defined by the lasing medium used to create the wavelength (measured in nanometers (nm)):

• Argon: 488 or 514.5 nm (not used for hair removal anymore)
• Ruby: 694 nm (not used for hair removal anymore; not safe on most skin types)
• Alexandrite: 755 nm (most effective, but safest on light skin)
• Pulsed diode array: 810 nm (for light to medium type skin)
• Nd:YAG: 1064 nm (for darker skin)

Pulsewidth is an important consideration. It has been observed in some published studies that longer pulsewidths may be safer for darker skin. However, shorter wavelengths may be more effective in removing hair.

Spot size, or the width of the laser beam, affects treatment. Theoretically, the width of the ideal beam is about four times as wide as the target is deep. Hair removal lasers have a round spot about the size of your finger (8-18 mm). Larger spot sizes help make treatments faster and more effective.

Fluence or energy level is another important consideration. Fluence is measured in joules per square centimeter (J/cm²). It's important to get treated at high enough settings to cause permanent damage to the hair follicles.

Repetition rate is believed to have a cumulative effect, based on the concept of thermal relaxation time. Shooting two or three pulses at the same target with a specific delay between pulses can cause a slight improvement in the heating of an area.

Epidermal cooling has been determined to allow higher fluences and reduce pain and side effects, especially in darker skin. Four types of cooling have been developed:

• Clear gel: usually chilled
• Contact cooling: through a window cooled by circulating water
• Cryogen spray: immediately before/after the laser pulse
• Air cooling: forced cold air at -34 degrees C (Zimmer Cryo 5 unit)

Multiple treatments, usually 3-8, have been shown in numerous studies to provide long-term reduction of hair. Current parameters suggest a series of treatments spaced at 3-12 weeks apart for most areas, although the timing of treatments has still not been standarized.

Number of sessions

The number of sessions depends on various parameters, including the area of the body treated, skin color, coarseness of hair, and gender. In addition, since hair grows in several phases and laser can only affect the currently actively growing follicles, several sessions are needed to kill hair in all phases of growth.

In general, it is necessary to foresee between 3 - 8 treatment sessions. Coarse dark hair on light skin is easiest to treat. Finer hair and hair on darker skin is harder to treat and may require more treatments. Certain areas (notably men's and women's faces) may require considerably more treatments to achieve desired results.

It's important to note that laser does not work on light hair and very fine and vellus hair. Electrolysis is the only permanent solution for those types of hair but has shortcomings such as possible scarring, expense, and discomfort, as noted above.

Intervals between sessions

Usually, treatments are spaced 3-12 weeks apart to start, although the spacing depends upon individual response to treatment. Instead of following an arbitrary schedule, you should wait until you have experienced shedding of the treated hairs, which should complete within 2-3.5 weeks, and see enough hair come in after the hair-free period to have another treatment. Treatment spacing also depends on area treated as hair cycles vary based on the body part. For example, women’s faces usually require more frequent treatments, whereas backs and legs require less frequent treatments.

Other uses

Hair removal lasers are effective treatment for pseudofolliculitis barbae (commonly called ingrown hairs or "shaving bumps"). 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.

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.

Risks

The use of large quantities of high potency topical anesthetics to large surface areas of the skin, particularly when applied under occlusion, such as under plastic wrap, may result in lidocaine toxicity and resulting arrhythmias, and is contraindicated. According to published reports, two women completely coated their legs in topical anesthetic cream while at home and then suffered a toxic reaction on their way to the laser clinics, which led to coma and then death.^[22]Risks include the chance of burning the skin or discoloring dark skin with the laser, hypopigmentation (white spots), and flare of acne. Some point to the lack of proper government regulations in many countries as meaning that patients are at risk of being treated by improperly trained staff.^[23]

Relative contraindications

Laser hair removal should be used cautiously, if at all, by patients in the following categories: Recently acquired dark tan; fine, light hair in people of color; blonde or red hair in areas with tan skin; patients who cannot afford or do not have the time for multiple sessions, because one treatment is rarely adequate.

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