Lasers set at specific wavelengths will selectively treat certain components of the skin, such as hair and vascular legions. This is called selective photothermolysis.

The GentleLASE is a long-pulsed alexandrite laser which pulses laser energy at a wavelength of 755 nanometers (nm). The laser light passes through the skin to the hair follicle, where it is absorbed by the pigment or melanin. (Melanin gives skin and hair color.) The laser energy heats the melanin to the extent that there is significant damage to the hair follicle, which can disable the follicle while leaving the skin unchanged.

To be even more technically specific, the 755 nm wavelength causes maximum selective energy absorption by the hair follicle's melanin and minimal absorption by the surrounding skin structures. Along with this, the laser pulse duration is controlled to be equal to or shorter than the thermal relaxation time of the hair, to help minimize the heat transfer to surrounding tissues.

The Candela laser systems are the only hair removal laser to feature the Dynamic Cooling Device. The DCD delivers a spray of cryogen on the skin's surface directly before the laser pulse. This cools and protects the skin and increases the comfort of the treatment.