All lasers work by producing light of a very specific wavelength. If the wavelength of the laser is matched to a target colour (such as the red of blood in the blood vessel), the energy of the laser is absorbed specifically by the target but not by the surrounding tissues.

The diode and the Nd:YAG lasers deliver a series of focused energy pulses generating heat for very short periods of time; this energy closes down the thread veins, without perforating them; it is rather like spot welding.

The pulsed dye laser delivers a larger spot of energy that heats target vessels in the area to destruction, causing bruises to appear. This effect makes the laser most suitable for red flares of vessels and those conditions that do not respond to treatment with the diode.

In either case, the damaged veins are gradually dissolved and removed by the body's immune system over several weeks after treatment.