Epilation performed by laser was performed experimentally for about 20 years before it became commercially available in the mid 1990's. Laser and light-based methods are sometimes called phototricholysis or photoepilation.

In addition to lasers, some light-based epilators use a xenon flashlamp which emits full-spectrum intense pulsed light (IPL). Treatment with this device is sometimes popularly referred to as laser hair removal, though the device is not a laser per se.

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.

Carbon, which is introduced into the hair follicle by rubbing a carbon-based lotion into the skin following waxing (this lotion is an "exogenous chromophore"). When irradiated by an Nd:YAG laser, the carbon causes a shock wave capable of mechanically damaging nearby cells.

Hemoglobin, which occurs naturally in blood (it gives blood its red color). It preferentially absorbs wavelengths from argons, and to a lesser extent from rubies, alexandrites, and diodes. It minimally absorbs the Nd:YAG laser wavelength.

Melanin is considered the primary chromophore for most lasers currently on the U.S. 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).

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

Ruby: 694 nm

Alexandrite: 755 nm

Pulsed diode array: 810 nm

Nd:YAG: 1064 nm

Pulsewidth is an important consideration. It has been observed in some published studies that longer pulsewidths may be more effective with fewer side effects. Recently, very long pulse or super long pulse lasers have been theorized to be safer for darker skin, but this has yet to be demonstrated in published data.

Spot size, or the width of the laser beam, affects treatment. Theoretically, the width of the ideal beam is about four times the as wide as the target is deep. Most lasers have a round spot about the size of your little finger (8-10 mm).

Fluence or energy level is another important consideration. Fluence is measured in joules per square centimeter (J/cm2).

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. 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: a newer experimental method

Multiple treatments have been shown in numerous studies to be more effective for long-term reduction of hair. Current parameters suggest a series of treatments spaced 4 to 6 weeks apart, but theoretically, there is a point of diminishing return where additional treatments will not cause additional loss.

Laser energy also gets less effective the deeper into the skin it must travel. Think of it like putting your hand over a flashlight. A little light penetrates the thinner skin (the reddish glow), but can't penetrate the thicker areas. Light that enters the skin is either absorbed or scattered and reflected back out of your hand. When this happens to a laser beam, this scattering is called attenuation. The more tissue light has to travel through, the more attenuation will occur. That means at deeper levels, less energy reaches the target.

Lasers can be useful for surface dermatological procedures like removing some kinds of tattoos and birthmarks like port wine stains. That's because the target is superficial and often even in depth and color compared to hairs. Hairs in any given treatment area can be widely variable in diameter, color, and depth. This poorly delineated target makes laser effectiveness hard to predict. The same amount of laser energy will have different effects on hairs with different widths. Some hairs are as deep as 7 millimeters. It's hard for a laser to be effective at those depths without overheating the upper skin.

Obviously, if a laser targets melanin, the less melanin you have in your hair means the less effective a laser will be. That's why someone with gray, red, or blonde hair is not as good a candidate for laser hair removal.

In addition, the more melanin in your skin, the darker it looks. Caucasians typically don't have much skin melanin, while Blacks have more. The laser doesn't distinguish between melanin in hair and melanin in skin. That means the more melanin in a skin, the more the laser is going to be absorbed by the skin. That's why someone with darker skin is not as good a candidate for laser hair removal.

Light skin and dark hair are the best combination for laser hair removal. The more closely your skin tone matches your hair color, the less likely you are to benefit from laser hair removal.