Tattoos can be wholly or partially removed by cosmetic surgical techniques, most commonly through the use of lasers. The laser reacts with the ink in the tattoo, and breaks it down. After this, the patient's body then absorbs the broken-down ink and the skin heals once more. The procedure can be expensive, and very painful (some say more so than the original tattoo) and often requires many repeated visits to remove a small tattoo. It also may not be entirely effective in leaving unblemished skin, due to the fact that tattoos also scar the skin to varying degrees, depending on how the tattoo was applied, the way the skin healed, and the area that was tattooed.
A newer method of removal is by tattooing glycolic acid into the skin with a tattoo machine: the acid pushes the ink to the surface of the skin in the scab, which is later removed. This method supposedly scars less than lasering. Glycolic acid is also used for facial peels; when used for tattoo removal, a lower percentage mix is used.
Another alternative for unwanted tattoos is to cover them up with a better tattoo. With the advent of laser tattoo removal, cover up tattoos are becoming less common. Many younger tattooists don't know how to or won't camouflage unwanted tattoos. An experienced artist can often come up with a design that incorporates and hides the existing tattoo.
More recently, many higher end shops and artists have begun using professional laser removal machines not to completely remove an unwanted tattoo, but to break down and lighten it so as to be easier to cover with a new tattoo. Usually after two or three treatments the old tattoo is eliminated enough to cover, all without the extensive damage to the skin that a complete removal would cause.
http://www.tribal-tattoos.co.uk/tattoo-removal.php