We've all come to accept that tattoos are permanent — no matter how hard we try to scrub, burn (not advisable), or laser off the remnants of regrettable ink. But despite the tattooing practice being in existence for some 5,200 years, scientists have never been able to pinpoint the exact reason the pigment lasts so long on the skin. Until now.
A new study published in the Journal of Experimental Medicine revealed that tattoos don't shed with the rest of your skin because the pigment is trapped deep in the dermis, thanks to a little-known immune system cell called a macrophage. Like the white blood cells that attack bacteria in your body when you have a cold, researchers discovered that macrophages rush to the puncture area as you're getting inked and immediately absorb the pigment.
While scientists unfortunately resorted to tattooing a green pattern on the tails of several defenseless mice (a cruel practice that's still very present in the beauty industry today) for the study, doing so did lend a few interesting conclusions. First, despite various, non-lethal efforts to kill off the cells that contained the tattoo, the macrophages worked so fast to engulf the color that the ink remained in tact. Second, this likely proves why laser tattoo removal take several sessions to complete. Since lasers break down ink particles, but don't target the macrophages, every time you zap, there's a string of new cells just waiting to swoop in and trap the pigment yet again. The equation for success then becomes, researchers hypothesized, to target both elements.
The study authors say they are hoping to work with dermatologists to test this theory on humans in the future. In the meantime, maybe hold off on requesting a Kim Kardashian cry-face design on your lower back unless you know you'll truly love it for 50 years.
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