Lasers erase tattoos by shattering ink into tiny pieces

Tattoo ink remains permanent because its particles are giants compared to your body's cleanup cells. When a needle deposits pigment into the dermis, your immune system dispatches white blood cells called macrophages to eat the foreign invaders. However, ink particles made of carbon black or titanium dioxide are often 200 nanometers wide—far too large for a single cell to engulf. Because these particles are chemically inert, they simply sit in place for decades, trapped within the skin's architecture like boulders that a gardener is unable to lift.