Why tattoos are permanent

NARRATOR: It's an art form that's been around for thousands of years. It shows no sign of slowing down. If you don't have them, chances are your friends, or at least your favorite barista, does.

Tattoos. This week, we're all about that ink. So think carefully about what you want on your body permanently. Then tattoo some knowledge to your brain.

Thousands of years ago, when hipsters of that era were getting tattoos, many different ingredients were used for inks. Different colors came from ground-up natural products like copper, ashes, graphite, tree bark, and woad.

JOEY: Woad!

NARRATOR: Today, our inks have evolved. Quick fun fact-- we still use so many different pigments for colors that if you have two different tattoos from two different places, there's a chance that ink in your right arm is made up of different stuff than that ink in your left arm.

No matter what the ink ingredients are, it's a straightforward recipe. A solid pigment creates the color and is suspended in a liquid carrier. Liquid carriers can include any one or a combination of the following-- water, witch hazel, glycerin, propylene, and alcohols, anywhere from ethanol to vodka to even Listerine. There's a wide variety of pigment ingredients, too. Here's some of the different forms of blacks, browns, reds, greens, blues, violets, yellows, and whites.

So why are tattoos permanent? As you might know, skin cells live for about two to three weeks, but tattoos last forever. And if you've ever thought that tattoo on your inner lip will disappear after six months, well, you'd be dead wrong. It will never disappear.

All right, then. To explain why tattoos are permanent, here's Rachel Feltman from the Washington Post's "Speaking of Science." And, conveniently, she's in the middle of getting a tattoo.

RACHEL FELTMAN: So right now, the tattoo needles, which have ink stuck between them, are puncturing my skin about 50 to 3,000 times a minute. They're going through the epidermis and into the dermis. And when they're making holes there, capillary action is actually drawing the ink down into the dermis.

The tattoo becomes permanent when my immune system tries to save me from all of these wounds that I am suffering. Basically, every time the tattoo needle makes a hole, macrophage cells will start to go towards the wound to try to close it up. And because the ink is a foreign invader, the macrophage cells gobble it up to try to get rid of it. But instead, those macrophage cells with bellies full of ink get stuck in the gel-like matrix of the dermis. And they stay there pretty much forever, which is why the tattoo stays visible and permanent.

NARRATOR: She makes it look so painless. So when your tattoo is brand new, the ink is in both the epidermis and the dermis layer of your skin. But as the skin heals, the wounded epidermal cells are shed and replaced with new, ink-free cells. This is why your tattoo looks more vibrant before it's done healing.

Your epidermis regenerates in about two to four weeks. Over time, tattoos will fade as a body's immune system slowly breaks down the alien pigment particles and the macrophages take them away to be destroyed. But for the most part, the ink will stay with you forever.