Olga Khazan wondered about how does tattoos stay in the skin if we lose almost one million cells dead skin cells per day. The explanation most people give is that it is under the skin where it cannot get washed away. However, the answer is more complicated than that. The permanency of tattoos are caused by the immune system.
Once the needle perforates the skin, it causes a wound, which will make the inflammatory system to respond. The ink that went into the dermis is eaten by macrophages. However, some macrophages do not return to the nymph nodes; they stay in the dermis; and with no way to dispose of them, they stay visible from the outer skin. Some of the ink stay in the gel-like part of the dermis while others are engulfed by fibroblasts, dermal cells.
At first, the ink also stays in the epidermis, but it gets removed gradually, either by UV light from the sun, and because your cells simply die and gets replaced. When the dermal cells die, they are replaced by new ones, but the ink stays. However, in time, tattoos do fade naturally, breaking down in particles gradually, so that macrophages can do its work again. Sun radiation also helps with the ink breakdown, but most of the pigmentation stays deep in the skin making it permanent.
But it does not have to stay there forever. Tattoos can be erased with the help of laser machines. These machines sends out a laser beam that will break down the pigmentation, black being the easiest to break down. The pigments gets small enough that the macrophages once again may do its work. It is not that easy to erase, but not impossible.
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