Amie SoloskyIn 2023, it was reported that 32% of Americans have at least one tattoo, a permanent piece of art designed and applied by tattoo artists. But what exactly makes these fun designs permanent? The science of tattoos is very interesting as it relies on a healthy immune system. First, the tattoo artist coats a sterile needle with ink composed of pigments, water, and rubbing alcohol. The needle gun is then turned on and the tattoo artist begins working. The needle gun allows the needle to puncture the skin about 100 times per second, 1.5 to 2 mm deep. This is equivalent to the depth of a penny, reaching into the second layer of the skin known as the dermal layer (or dermis, Figure 1).
Once the tattoo ink penetrates the skin, the host’s immune system gears up to begin its attack on this foreign substance. First, a clot forms at the puncture wounds. Over time, the skin tissue swells, causing immune system cells known as macrophages to travel to the site of the wound. These macrophages are responsible for removing foreign substances and debris such as bacteria, dead cells, and in this case, ink particles. The macrophages attempt to remove the tattoo ink particles by digestion. Interestingly, they cannot digest the ink because macrophages typically use acid to do so, which is no match for the tattoo ink. Digestion is especially difficult due to the high amount of ink present. Instead, the macrophages are unable to do anything with the ink besides store it until they eventually die, anywhere from months to years later.
For a long time, it was debated what occurs once macrophages consume the tattoo ink. However, a study in 2018 revealed that macrophages actually go through cycles of swallowing ink and then releasing it after death. Therefore, the longevity of the tattoo is due to the macrophages repeatedly swallowing the ink, dying, and then new macrophages repeating the cycle over and over again.
But why do tattoos fade?
Tattoos fade due to other immune cells known as fibroblasts, which are the cells that form scar tissue. Over time, this scar tissue gets pushed deeper and deeper into the skin, causing the tattoo to appear faded. This occurs naturally and takes many years. Another way tattoos fade is from exposure to UV rays which break down the pigments in the ink, therefore sunscreen is essential for preservation. If you do decide to get a tattoo, thank your immune system for all the hard work it is doing to help keep you safe (and make your tattoo last)!
