How do laser treatments work?

Laser treatments for the skin work on a principal called "Selective Photothermolysis." Selective photothermaolysis is a concept that revolves around the fact that each different type of laser (different wavelength) has a specific target.

For some lasers the target is melanin (hair and skin pigment), for others it is hemoglobin (blood) and for others it is water. This is why some lasers like the Pulse dye laser are used for Rosacea and Port Wine stains (hemoglobin target), while others like the the q-swtiched Nd:Yg laser are used for sun spots and tattoos (melanin and pigment).

During selective photothermolysis the target is heated and destroyed while the surrounding skin tissue is preserved. This is how we can selectively target something like spider veins and not damage the skin surrounding the vein.