So you got a tattoo. And now, for any number of reasons — it was a drunken mistake, it looks weird on your body, you simply don’t want it anymore — you want to get rid of it. But it’s permanent, right?

Tattoos might seem permanent, but they’re actually not technically. Tattoo removal services are seeing a spike: At least one in four people regret their tattoos, and it’s grown to be a $3.5 billion industry. It makes sense, given the fact that about 40 percent of Millennials have tattoos.

But how does it work? Probably the biggest misconception about tattoo removal is that the process pulls the ink out of your skin. It doesn’t. Ink is a foreign agent to your body, and therefore your skin is always trying to work it out, the same way it would react to a splinter. The reason it can’t is because the ink particles themselves are too large to squeeze through the surface. The lasers used by tattoo removal specialists work by breaking down those particles into even smaller particles, fracturing the ink and causing it to essentially break down until the particles are small enough to pass through the subcutaneous level of skin into the lymphatic system. From there — assuming you’re decently hydrated — the ink is simply flushed out with the rest of your urine.

That process takes at least two weeks to get underway. Tattoo removal sessions are generally spaced out six weeks or so apart, and the efficacy of the process depends not just on the size and density of the tattoo itself, but on what colors it comprises and, kind of weirdly, the general health of its owner.

The common black ink also happens to be the easiest to remove, requiring about five or six sessions. Greens and blues, however, could take as many as 10. The lasers actually operate at different wavelengths to fade the different colors. Matt Russo, founder of InkAway Laser Tattoo Removal, said a Class 4 laser operating on a 1064 wavelength is the most common, since that’s the one that treats basic black. A 532 wavelength will sort out your oranges and reds, while you need a 694 wavelength to get at the tougher green/blue/purple spectrum.

“Sometimes you can taste the metal in your mouth,” Russo said. “But [the pain is] comparable to when you get the tattoo, it’s that same feeling. A numbing cream helps about half the time. But then its like getting a new tattoo every six weeks.”

Russo also explained that an older person, or perhaps a heavy drinker, might need a year of treatments to see good results. Younger clients, triathletes, people who lifts weights or take the kind of supplements you might be otherwise inclined to make fun of, will actually see their tattoos fade much more quickly, since their lymphatic systems are more effective. Those demographics might be done in as few as four sessions, but the average American will probably need eight or 10.

Photos via Getty Images / Scott Eisen

Kastalia grew up in Littleton, Colorado, and has a journalism degree from the University of Southern California. She spent the past year and a half backpacking around the world and recently moved to New York. Her RTs = unwavering personal convictions.