The ink from a tattoo removed by laser goes to the lymph nodes. These are bean-shaped organs distributed throughout the body, but with a higher concentration in the neck, armpits, and groin.
The ink particles can be processed by the lymph nodes, subsequently broken down and excreted through urine. However, larger particles may accumulate permanently in these glands.
When a tattoo is made, the needle pierces the skin hundreds of times per second, depositing the ink in the dermis. The immune system recognizes these particles as foreign bodies and attempts to destroy them. Macrophages, defense cells, absorb the ink and try to dissolve it internally, but the particles end up trapped inside the cells.
Furthermore, fibroblasts, which are responsible for the structure of the skin, also absorb part of the pigment, which explains why the tattoo remains in its original location without spreading.
To remove the tattoo, what macrophages could not achieve must be done: disintegrating the ink particles. This is accomplished by applying high-frequency lasers. The choice of laser depends on the color of the pigment; for example, green lasers are used to destroy red pigments, while green pigments require red lasers.
The laser heats the ink particles in the epidermis, raising the temperature between 200°C and 600°C, which causes the burning sensation. The particles fragment into countless tiny, superheated pieces.
Part of this ink is reabsorbed by macrophages and carried to the lymph nodes via the lymphatic system, which functions as a second circulatory system. The final destination of larger particles is to remain in the lymph nodes indefinitely. Smaller particles enter the bloodstream, are filtered by the kidneys, and some are eliminated through urine.
However, another fraction of the ink goes through the same initial cycle, returning to become retained in the skin. For this reason, multiple laser sessions are necessary to completely eliminate the design.