Tattoo ink sits in particles too large for the body to naturally break down and clear on its own. The Q-switch laser delivers extremely short, high-intensity pulses of energy that are absorbed by the ink itself, causing it to fracture into much smaller fragments. Once shattered, these smaller ink particles become small enough for the body's immune system — specifically, cells called macrophages — to gradually absorb and flush out through the lymphatic system over the following weeks. 
Different ink colors absorb different laser wavelengths, which is why darker inks (like black and dark blue) typically respond fastest, while lighter colors (yellows, greens, light blues) often require more sessions or a different wavelength setting to fully clear.