The word photothermolysis comes from three Greek root words -- "photo" meaning light, "thermo" meaning heat, and "lysis" meaning destruction. Selective photothermolysis therefore refers to the precise targeting of a structure or tissue using a specific wavelength of light with the intention of absorbing light into that target area alone. The energy directed into the target area produces sufficient heat to damage the target while allowing the surrounding area to remain relatively untouched.
In the world of plastic surgery, this term is applied to treatment of the skin with lasers. The “target” of this type of laser is determined by its color. For instance, when selective photothermolysis is used in laser tattoo removal, the laser targets specific colors. Therefore, different lasers (or different settings on the same laser) are used to break up different colors of ink.
This explains why a pale-skinned patient with a black tattoo will usually get the best and fastest results. The laser attacks the dark ink and leaves the pale skin around it intact. It also explains why ink colors which are closer to skin colors (browns, yellows, pinks) are more challenging to remove, and why laser hair removal is easiest on a person with fair skin and dark hair.