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Before we get into the process of tattooing, we first need to look at the skin.
The skin is comprised of three main layers the epidermis, dermis, and subcutaneous. The epidermis is the uppermost layer that’s main job is to protect. The epidermis sheds and regenerates the fastest. The dermis is the second layer that includes the hair follicles and glands as well as blood vessels. The third and final layer is the subcutaneous layer which includes all of the fatty tissue, this is meant to insulate.
When you ask most people about how tattoos are done, they may get a few things wrong. A major oversimplification of the process is that the tattoo machine injects ink into your skin deep enough to permanently stay in the skin. This however is not correct; a tattoo machine is more like the nib of a fountain pen rather than a syringe. When the artist dips the needles into the ink the ink becomes suspended at the end of the needles and capillary action does its magic. Capillary action refers to movement of water (or in this case, ink) within porous material (the skin). This all sounds pretty painful, but the needles are only penetrating 1/16ths of an inch into your skin, that is smaller than a grain of rice. This is to ensure that the ink particles are nestled safely in the dermis. If the ink particles were only piercing the epidermis the tattoo would essentially shed off due to the rapid shedding and regeneration of the epidermis. Now that is how the ink is deposited into the skin but how on earth does it stay put?
You may believe that the ink is deposited into the skin cells however there is a little bit more to this. Initially it is deposited into the skin cells however it is the immune systems microphages that are the stars of the show. Microphages are white blood cells that ingest foreign and cellular waste. These are the guys that come rushing in when you get a cut or a scape, so it is no surprise that microphages come in when you are getting pierced with a needle continuously. These microphages end up eating the ink and due to their cellular membranes, the ink is kept suspended in these microphages for years to come. The next question you may ask is but don’t cells die? Of course, they do. This is why when a microphage dies the ink is released back into the skin cells however due to the ink still being foreign debris there are new microphages at the ready to eat the ink again, this process continues for the life of your tattoo. Your tattoo isn’t just the remnant of a battle between your love for body art and your immune system. It’s a war that never stops. It’s pretty metal if you ask me.
Green tattoo pigment is taken up by dermal macrophages (left). The pigment is released when these cells are killed (center) but, 90 days later, is taken back up into new macrophages that have replaced the old ones (right). Baranska et al., 2018