Your body basically treats a tattoo like it’s an infection. Ink is injected into the skin where it is gobbled up by immune cells called macrophages as if it’s an invading pathogen. Macrophage, incidentally, translates to “big eater” in Greek.
The skin goes through a cycle of constant regeneration and old skin cells, including macrophages, die off to be replaced with shiny new ones, so you might assume that tattoo pigment would fade and disappear with the dying macrophages. Yet, clearly, it doesn’t because we all know a tattoo lasts a lifetime. Now, a team of scientists from Aix Marseille Université, France, think they know why.
Research published in the Journal of Experimental Medicine found that the ingested ink is released into the skin's dermal layer when a macrophage dies to be soaked up by the surrounding cells. It continues this cycle for, well, ever, which essentially means that your tattoo renews as the skin does.
This disproves previous theories that tattoo pigment stains the skin, thus linking a tattoo’s permanence to cell longevity rather than cell regeneration (as has turned out to be the case).
“We further demonstrated that tattoo pigment particles can undergo successive cycles of capture–release–recapture without any tattoo vanishing,” the study's authors explained in their paper.
“Therefore, congruent with dermal macrophage dynamics, long-term tattoo persistence likely relies on macrophage renewal rather than on macrophage longevity.”
To test the theory, the team inked mice tails with green stripes before removing their macrophages to see how it affected the quality of the pigment. The ink appeared identical to how it had been before the treatment, suggesting that the pigment had been released into the dermal layer before being adopted by new skin cells.
The results were confirmed when the team transplanted a tattooed skin graft from one mouse to a second (albino) mouse. Six weeks later, macrophages in the albino mice were absorbing the tattoo pigment as if it were their own.
Aside from being a fascinating piece of research that helps explain how your tattoo lasts so long, it could prove useful for anyone wishing to remove one they now regret – perhaps an ex’s name or an unfortunate souvenir from Spring Break 2007.
While the researchers admit that the next stage of testing needs to confirm whether or not this cycle of capture and release applies to humans as well as mice, they do suggest that laser tattoo removal could be more effective when used alongside the surgical removal of the inked-up macrophages.