Skin Deep Science – How Do Tattoos Work?

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  Last updated September 12, 2017 at 11:46 am

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The most frequently asked question about tattoos has to be – how do they stay in your body? It all has to do with the structure of skin and the immune system. 


Have you ever thought about getting a tattoo? If you do, you’ll be in good company – almost 1 in 5 Australians are inked. As tattoos become more common and it’s often not necessary to cover up in the workplace, you may have considered declaring your love for your favourite Pokémon with a little piece of art where it will never leave you. So how does it work?



Our skin is made up of three layers – the epidermis, which forms a protective barrier against infections; the dermis, which contains the hair follicles, sweat glands and blood vessels; and the subcutaneous fat layer, which attaches the dermis to the muscles and bones underneath. When you are tattooed, the needles penetrate through the epidermis to the dermis. Once in the skin, the body reacts to the ink just like how it would with any foreign invader – it sends a horde of white blood cells to remove them, and the tattooed areas will swell and turn red and eventually begin to scab over and flake.


But ink particles are much larger than white blood cells, and while some of the smaller particles will be removed, the majority will sit in the skin forever more, untouchable.


What’s even cooler is how the ink is injected into the skin – there’s some nifty physics behind it. Tattoo needles don’t work like the needles used in vaccinations where there is one hollow tube of metal. Tattoo needles have at least three sharp points for fine lines, and many more for shading. The ink is held in place between them, much like how water can be sucked up a very narrow gap between two flat pieces of glass. This is called capillary action. Once the needles puncture the skin, the ink is drawn down into the puncture wounds due to a combination of adhesive forces (where the ink molecules are more attracted to the skin than to themselves) and surface tension (so that the ink moves through the puncture wound as a fluid and not just the ink molecules that are in contact with the skin) until it is deposited in the dermis.


Once you’ve gotten your tattoo, there is still a risk of infection and blowouts. If the tattoo artist accidentally injects the ink too shallowly, into the epidermis, your tattoo can turn into an ugly, discoloured blob as the ink is carried away by your body’s normal regenerating process. And if the needle is inserted too deeply the ink can spread erratically through the underlying layers of skin. Infections can also arise from inadequate equipment sterilization, improper aftercare or an unclean environment, and in some cases have led to sepsis and death.


The most famous archaeological evidence of tattoos can be seen on Ötzi the Iceman dating back to 3100 BC, but earlier cases do exist. Tattooed mummies have been uncovered in regions around the world from Egypt and North Africa to Siberia and Alaska, but they weren’t always done for cosmetic reasons. Throughout history, they’ve been used as displays of high status, markers of slavery, and as cultural and religious symbolism; tattoos were also believed to imbue upon its wearers spiritual and medicinal powers – mummies suffering from diseases like rheumatism have been found with tattoos on areas of the body which would not have been easy to display, such as behind the knees and around the abdomen, and thus researchers believe they were placed there for healing purposes. Traditionally, tattoos were applied using a sharp instrument, typically made of animal bone or bronze, dipped in ink made from ground charcoal. The process was – unsurprisingly – exceedingly painful and the risk of infection high.


Don’t let all this scare you away from tattoos, however. Done properly, you could end up with amazing tattoos like this and this . And even the fact that you want a tattoo could say something about you: a 2016 study found that people with tattoos rated higher in extraversion, which could translate to “higher levels of task performance and proactivity in the business world”. As accepting attitudes take the place of the social stigmas towards tattoos, you’re bound to see more examples popping up in your day-to-day life, including this awesome mix between a tattoo and a health tracker. And perhaps the question will no longer be whether or not you should get a tattoo, but where it should be placed (an equally difficult question, I can assure you).


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About the Author

Linda Quan
Linda is a physics and chemistry graduate who loves to write in her spare time. She is also addicted to coffee and online shopping. On cold, moonless nights, she often ventures out with her camera to take pictures of the stars. You can find her on Instagram @duoettria.