How do tattoos stay permanent?
Contrary to popular belief, tattoo needles don’t “inject” ink into the skin.
When you sit down to get your first tattoo, you won’t see anything like a syringe-like needle like one you would find at the doctor. Instead, a tattoo machine consists of a group of very small, separate needles bundled tightly together to hold ink between them. Think about how a paintbrush holds paint between the hairs of the brush. (And exactly how an artist dips their brush into paint, the tattoo artist will dip their needles into an inkpot. One dip will last them a couple of strokes until they have to dip again.)
The needles puncture your epidermis, or your outer layer of surface skin, 50 to 3,000 times per minute. The epidermis contains tiny holes that find their way into the dermis, which is the inner, thicker layer of skin underneath the surface skin. (The dermis is what contains blood capillaries, sweat glands, and nerve endings — which is also why tattoos can be very painful.) The ink from the needles is pulled down these holes into the dermis by what is called capillary action.
Capillary action refers to movement of water (or in this case, ink) within porous material. The porous material in this case is the epidermis, with holes leading down to the dermis layer below. Ink molecules are cohesive, meaning they like to stick together, and adhesive, meaning they like to stick to other substances. When the adhesion to the walls of the pores is stronger than the cohesion between the ink molecules, capillary action will cause the ink to travel down the holes.
So essentially, the ink is drawn into the inner layer of skin through capillary action. Needles aren’t “injecting” ink into your skin — needles are simply puncturing your skin, and physics are naturally leading the ink deeper into your dermis.
Once the ink is in your dermis, your body will sound the alarms. After all, you are sustaining a wound — the skin is ruptured, and foreign particles (the ink) are finding their way inside you. Normally, when something damages your skin, a swarm of white blood cells swoop in to fight infection and repair the rupture. They surround the foreign particles, absorb them, and then break them down into small pieces. The small pieces are then released into the blood stream to be disposed of.
However, the particles of the ink are simply too large for the white blood cells to break into smaller pieces. Once they engulf the ink, they can’t move. They are forced to float forever in the gel-like matrix of dermis, and the tattoo is there to stay. Over lengthy periods of time, the white blood cells may be able to slowly break the ink particles down, which is why tattoos can fade over time.
When you hop off the chair with your fresh, newly added tattoo, ink remains in the epidermis as well as the dermis. The ink in the dermis will never go away — but the ink in the epidermis will shed with the wounded cells, and be replaced with new ink-less cells. Once this healing process has finished in 3–4 weeks, your tattoo won’t hurt anymore, but it won’t look quite as bright and clear as it did before.
