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, thereby heating up the basal stem cells in the follicle which causes hair growth, the hair follicle, while not heating the rest of the skin. Light is absorbed by dark objects but reflected by light objects and water, so laser energy can be absorbed by dark material in the hair or skin, with much more speed and intensity than just the skin without any dark adult hair or melanin.

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 hair with color such as black, brown, or reddish-brown hair or dirty blonde can be removed. White hair, light blonde and strawberry blonde hair does not respond well. Laser works best with dark coarse hair. Light skin and dark hair are an ideal combination, being most effective and producing the best results.