Today's science post is all about a subject near and dear to my heart, namely tattoos. I love my tattoos and want copious amounts of them. The only thing holding me back at the moment is spousal acceptance, which is a force stronger than any in the universe. Our question of the week comes from my good friend Andy who asks:
Why do tatoos persist without spreading out or dissolving?
An excellent question, and proof to all of you out there sitting on your own questions, that I do take the time to answer reader requests. So send 'em in!
This is a pretty interesting question and gets to the inner workings of our biggers organ, namely our skin. Your skin is comprised of three layers, the epidermis, the dermis and the hypodermis. The epidermis is the skin you can see. Cells from this layer routinely work their way from the bottom of the epidermis up to the surface where they are sloughed off and feasted on by dust mites as you sleep. Some disgustingly high percentage of dust is actually human skin cells, which freaks me out to no end. The next time you're dusting, think about how most of what you just picked up is what stayed behind from Aunt Mabel's last visit. Ew. If your tattoo ink was deposited solely in the epidermis, it wouldn't be the permament testament to your love of Dokken that it is today.
Instead, tattoo ink is deposited in the dermis, which is the layer that gives skin it's elasticity. The dermis is comprised of all of the fun parts of your skin, including sweat glands and hair follicles. You don't get much more fun than sweat glands. Hoo boy. The dermis is also the home to fibrocyte cells, dendritic cells, macrophages, and mast cells. The first cells, fibrocytes, are responsible for proteins that establish the network of connective tissue that keep the dermis together. Those last three cells, dendritic cells, macrophages, and mast cells, help keep the dermis's immune response working.
When you get a tattoo, your epidermis and dermis are punctured many, many times by the buzzing tattoo needle and ink particles are deposited in the top most layer of the dermis. At this point, your body's immune response takes over. Macrophage cells and other phagocytic cells head to the area, find all these ink particles in the dermis, and proceed to "eat" the ink particles. As a result, the ink particles are enveloped by the macrophage and other phagocytic cells. As the tattoo heals, the cells containing the tattoo ink are trapped in the rebuilt connective tissue. For about a month after the tattoo, some ink particles escape up through the epidermis, but by 2 - 3 months, all of the ink is safely trapped in the dermis. This helps to explain why your nice, vivid tattoo becomes somewhat less vivid 2 - 3 months after its application, revealing any areas that need to be touched up.
Over time, the cells containing the ink move deeper into the dermis, and some of the cells migrate to the lymph nodes to say "Hey! Look what I captured!" This helps to explain why tattoos fade over time, however there's no clear answer to this question. Presumably, once all the diseases in the world are cured, science will turn it's eye to the important questions of tattoo fading.
So, to answer Andy's question simply, the reason that tattoo ink doesn't spread out or dissolve is because the ink is trapped in immune system cells that are themselves trapped in the fibers of the skin as the skin heals.
The other thing to take away from this post, as anyone with a tattoo can tell you, is that the care you give your tattoo immediately following its application is crucial to the health and longevity of your tattoo. The better care you can give your skin, such as moisturizing and proper application of antiobiotics, the better your body can focus on consuming and trapping the tattoo ink, rather than fighting off other infections or other damage to the skin. Similarly, this outlines why sun damage is so bad for tattoos. Sun damage kills skin cells, requiring the immune system cells to leave the dermis, where they're keeping the ink, and tend to the cells being killed by our good buddy Mr. Sun. For those with external tattoos, keep 'em moisturized and keep 'em sunscreened. That way you can have them well into your golden years, where they'll act as a constant reminder of when you were young and stupid.
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