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This is what laser tattoo removal looks like

Destin Sandlin, host of the YouTube show Smarter Every Day, recently devoted an episode to the very interesting science of tattooing — even filming a tattoo needle piercing someone's skin at 3200 frames per second.

His newest episode, above, is even more fascinating: it breaks down the science of tattoo removal.

Why tattoos don't just fade away

As Sandlin points out in the video, getting a tattoo involves having pigments injected into your dermis, the layer of skin just below your epidermis, which is on the surface.

dermis diagram

(Livingdeadlivingart.com)

Typically, your body's immune system eliminates all foreign substances that make it down to this layer, but some of the ink droplets are simply too big for your white blood cells to break down easily. (In the video, Sandlin even looks at his blood cells and ink droplets under a microscope to show the huge size difference.)

Over time, the white blood cells do have a tiny bit of success in eating away at the ink droplets and carrying pieces of them away — which is why tattoos fade slightly and get less sharp over the years — but for the most part, they're permanent.

How lasers remove tattoos

About 21 percent of American adults currently have tattoos. And polls have shown that about 14 percent of these people regret getting them.

One solution is laser tattoo removal, which was invented during the 1980s and has become increasingly popular over time — nearly 100,000 removal treatments are now performed annually.

Lasers can break up the large ink droplets by intensely heating them for very short periods of time (the laster in the video, for instance, turns on and off periods as short as one trillionth of a second). This causes one side of the droplet to expand. Because the other side doesn't expand equally, the droplet breaks apart, and the smaller pieces can then get carried away by your white blood cells over time.

The process still isn't perfect — it can leave scarring and typically takes multiple sessions — but it's still a pretty amazing marvel of modern science. Think about it: centuries ago, we figured out how to inject permanent inks into our skin solely for decorative reasons. Now, we've figured out how to use lasers to destroy them when those designs don't turn out exactly as planned.

Be warned, though: getting a big tattoo removed can take a long time. And people who've done it confirm that, as you might imagine, having a hot laser blasted at your skin hurts like hell.

Read moreThis is what happens when a tattoo needle pierces your skin

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