Tattoos have been a part of human culture for over five thousand years, and having recently gone under the needle myself (I got a little rocket on my upper back, if you’re interested), I found myself wondering what it is that makes tattoos permanent. In my search for information, it became apparent that there are two main factors: the composition of the tattoo ink and the depth at which it is injected.
As you probably know, tattoos are drawn using a mechanised needle that repeatedly punctures the skin at a rate of anywhere between fifty to three thousand times a second. This needle penetrates to a depth of around two millimetres, depositing the ink into the layer of skin known as the dermis. The skin is made up of three main layers, and as the thickest layer, the dermis is sandwiched between the others (the epidermis and the subcutis). It is made up of a variety of fibrous and dense connective tissues, and unlike the epidermis, it does not shed cells. Due to this, the ink deposited there is not degenerated by the day-to-day shedding of skin cells (usually at a rate of around forty thousand cells per day). However, this does not mean that the dermis does not undergo constant degeneration. One of the reasons that tattoos fade over time is the cyclical process of cell death and regeneration that occurs in all parts of the body.
Now, we all know that the body does not necessarily take kindly to being repeatedly attacked with an ink-filled needle. As soon as the nerves send reports of the invasion to the central nervous system, thousands of white blood cells are deployed in order to remove the invading ink particles and heal the wounds. Normally, white blood cells break down any offending foreign bodies and transport them to the lymph nodes where they can be disposed. However, tattoo ink is made up of a variety of compounds, and the majority of them are too large for white blood cells to remove. This doesn’t stop them from trying though; tattoos are constantly under attack from the immune system, and this is part of why they tend to fade and blur over time. Interestingly, this plays a large role in how laser removal procedures get rid of unwanted tattoos. The laser is used to break down the embedded ink into little pieces that are small enough for the white blood cells to naturally remove.
So, there you have it. The creation of a permanent piece of art relies on two main factors – the chemical composition of the ink used and the depth at which it is embedded into the skin. Pretty funky.