Laser treatment works on the principle that dark objects absorb more light. Think about going out on a sunny day wearing a black T shirt versus going out on the same day wearing a white T shirt. The white T shirt reflects light and stays cooler, but the back T shirt absorbs light and makes your body feel hotter. Similarly laser energy is absorbed by dark material present in the skin. This dark target matter, or chromophore, can be naturally-occurring or artificially introduced.

The laser beam used in the laser hair removal device is directed at the hair follicles. The dark pigments in the follicle absorb the laser light energy, but the relatively less pigmented skin does not absorb the light energy; in fact, energy dissipates. The follicle absorbs more and more energy and heats up. Ultimately the follicle dies and can no longer grow hair.

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. Laser and light-based methods are sometimes called phototricholysis or photoepilation.

Melanin is considered the primary chromophore for most lasers currently available in the U.S. market. However, if there is little or no melanin pigment in the hair follicles then pigment can be artificially introduced to the hair follicle. Laser light can also be absorbed by other kinds of pigment in the skin. Consequently, hair removal lasers can selectively target several chromophores:

1. Carbon, which is introduced into the 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.

2. 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.

3. Melanin, which 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). Eumelanin is better targeted by lasers as it is a darker pigment.