Michael: Nearly one in five people in America has a tattoo. So these permanent, portable pieces of art are clearly an important part of our culture -- but how do they work? What makes a tattoo permanent, and can you really get rid of it?

Well, tattoos work by taking advantage of the structure of your skin, and the composition of the ink that’s used. Your skin, for starters, is made up of three main layers of cells. On top, there’s the epidermis, which is exposed to the environment. Below that, there’s the dermis, and it’s full of hair follicles and sweat glands. And below that, you find the subcutaneous layer of fat and connective tissue.

A tattoo needle drives the ink all the way through the epidermis. But it doesn’t actually inject the ink -- instead, it’s coated with pigment, kind of like a paintbrush.

And the ink is absorbed through capillary action -- it just gets sucked down through your tissues into the dermis. This is deep enough that the ink won’t just flake away as you lose skin cells from your epidermis over time. And it’s also why getting a tattoo hurts. The dermis is full of nerve endings that sense pressure, temperature, and pain. So jamming a bunch of tiny needles into that layer activates at lot of those receptors.

Some people say that getting tattoos on boney areas hurts the most, because there’s no fat to act as a cushion, but there’s not really any scientific evidence to back that up. You can probably safely assume that your most sensitive body parts -- like the hands and face -- would be pretty painful to have tattooed, because they have the highest density of nerve endings.

Now, even though getting a tattoo can be pretty painful, many tattoo artists recommend that you avoid taking painkillers -- even aspirin -- before your session. That’s because those drugs can thin your blood, which makes the tattooing process more difficult.

Thinner blood means that the needle causes more bleeding, making it harder to see the area being tattooed, and that just makes things harder for the tattoo artist. So save the aspirin for after your art is done. And it’ll take a few weeks for your skin to heal.

Getting a tattoo triggers an immune response in your body, which tries to attack the ink as if it were an infectious invader. Normally, your white blood cells clean up after an injury, breaking down and gobbling up any foreign matter. And your white blood cells do manage to clear away some of the smallest particles of ink, which is why a new tattoo fades in the first couple of weeks.

But most of the pigment particles are too big to get eaten up and cleared away. So whatever your white blood cells can’t eat up gets absorbed by nearby connective cells called fibroblasts -- and the ink just sorta hangs out in there. Forever. Which is why tattoos are pretty much permanent. Mostly.

Fact is, even the most awesome tattoo will fade with time. As your skin ages, your fibroblasts die off and are replaced with new ones, so over time, the ink migrates a little as the cells turn over. Fading can also be caused by sun exposure -- the UV rays in sunlight break down the tattoo pigment, so more of it can be cleared away by white blood cells. And of course, if you end up with a truly terrible tattoo -- or if maybe you just don’t love Limp Bizkit as much as you used to -- we do have the technology to erase your tattoo. Mostly.

Laser tattoo removal works by using heat to break up the ink-pigment particles into even smaller pieces. Then, your white blood cells can finally clear them away, just like they always wanted. But the color of your tattoo can determine how hard it’ll be to remove.

Black tattoos tend to be the easiest to get rid of, because they absorb almost all wavelengths of light, so they heat up and break apart when treated with pretty much any wavelength. Other colors -- like red, green, blue, and white -- require special lasers, to make sure that the wavelength being used is the one that will be most easily absorbed by the pigment.

But even with the proper laser, tattoo removal doesn’t remove all of the ink -- and on top of being extremely painful, it has its own risks, including scarring. So if you’re going to get a tattoo, don’t bank on being able to get rid of it if you change your mind! As tattoos become more mainstream, we can hope that we’ll be able to develop better inks and improve our removal techniques. But in the meantime, like I always say, think before you ink.

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