From elaborate designs and sports team badges to the names of loved ones, tattoos come in all shapes and sizes. Their popularity has increased in the past 20 years, with 29 percent of the population of the United States reporting to have at least one tattoo.
But the inks used in tattoos are actually not developed for use in humans.
They are mostly made for other applications, such as the car paint or printing industries. The U.S. Food and Drug Administration (FDA) have, in fact, not approved any pigments for tattoos, and skin reactions to tattoos are not uncommon.
Although some tattoo inks are known to contain carcinogens, there is no concrete evidence that the chemicals in tattoo ink can cause cancer.
Solid needles are used to deposit ink into the deep layer of the skin. The body recognizes tattoo pigments as foreign particles and tries to clear them from the skin, but the chemistry of the ink used in tattoos makes this process quite difficult for the body. Hence, most of the color stays in the skin.
But why is it necessary to inject the ink so deeply?
Pigments are lodged in the dermis
The tattoo needle punctures your skin around 100 times per second, with the aim of depositing the ink in a region of 1.5 to 2 millimeters below the surface of the skin. The reason for this depth of penetration is to bypass the outer layer of the skin, or the epidermis.
This part of the skin constantly renews itself. Every day, thousands of epidermal cells are shed from your skin and replaced with new cells. Ink injected into the superficial skin layer would simply come off within 3 weeks.
In order to give the ink a permanent home in your body, the tattoo needle must travel through the epidermis into the deeper layer, or the dermis. Nerves and blood vessels are located here, which is why getting a tattoo hurts and your skin tends to bleed.
The bleeding is part of the skin's natural defense against injury. The result is an influx of immune cells to the site of injury.
Macrophages are specialized immune cells, whose job it is to engulf foreign particles and clear them from the tissue. But this process is only partially successful when it comes to tattoo ink.
Some macrophages loaded with ink particles remain in the dermis, while other pigment particles are taken up by the main dermal residents, which are called fibroblasts. Clumps of pigment particles have also been found to stick between the dense collagen fibers of the dermis.
Although every new tattoo will display some pigment loss, the majority of the ink will stay in the skin. A study in mice reported that 42 days after tattooing, 68 percent of the dye was still located at the injection site.
But where is the rest of the ink?
Colorful lymph nodes, remote destinations
In most cases, macrophages carry the ink particles to the lymph nodes closest to the site of the tattoo. Because the cells cannot break down the particles, they become lodged there. The side effect is that the lymph nodes take on the same color as your tattoo.
There is also some evidence to suggest that tattoo ink particles can travel through the blood and become lodged in the liver.
So, next time you opt for a tattoo, remember that it might not just grace your skin; it may also impart your internal organs with a unique color display.