The human body recognizes ink particles as foreign objects (porphyrins) causing white blood cells to attempt to break down and eliminate them. Because ink particles are so much larger than the white blood cells, the blood cells are inefficient at removing the tattoo ink, yet the body will forever work to eradicate the foreign substance which results in a tattoo that very slowly fades, but never disappears completely; ink particles unable to pass through lymph nodes; and the body being in a constant state of inflammation which could result in a weakened immune system.
Laser tattoo removal is by far and wide the most popular method for removing tattoo ink due to its high success rates and lack of serious side effects. Multiple treatments are usually required and although laser removal is highly successful, not all inks can be removed completely 100% of the time given the inconsistencies in inks.
Tattoo inks are not regulated by the FDA and many contain metals.