A laser is a device that produces an intense beam of light that has one particular color (wavelength). Laser light does not affect human tissue until it is absorbed. Whether tissue absorbs laser light depends on the tissue and the color of the light. For example, blood vessels absorb yellow, blue, and green light best, so lasers of these colors are used to selectively target blood vessels in the treatment of vascular growths. Other colors are used to target different conditions. Laser beams may be continuous or briefly pulsed in individual flashes. The pulse duration helps determine the effect of the laser beam.

Laser treatments are sometimes combined with photodynamic therapy, in which certain light-absorbing chemicals are applied to the skin or given by vein (intravenously). When these chemicals are struck by laser light, they absorb the laser energy and help destroy tumors.

Blood vessel growths, such as hemangiomas, and malformations, such as port-wine stains, may be treated with laser therapy. Laser therapy is also used to remove unwanted hair, tattoos, skin discoloration, scars due to acne, or sun damage.