Lasers work by producing short pulses of intense light that pass harmlessly through the top layers of the skin to be selectively absorbed by the tattoo pigment. This laser energy causes the tattoo pigment to fragment into smaller particles that are then removed by the body's immune system. Researchers have determined which wavelengths of light to use and how to deliver the laser's output to best remove tattoo ink. (If you're wondering if the laser might also remove normal skin pigment, don't worry. The laser selectively targets the pigment of the tattoo without damaging the surrounding skin.)
