With more and more people getting tattoos, it makes sense that the market to remove them has increased dramatically over the years. Almost everyone knows about laser tattoo removal because it’s really the only way for someone to scrub their skin clean of a piece of artwork that was meant to remain permanent for life. Although, very few know the exact science of how laser tattoo removal works or that the final step in the process is for someone to poop out the ink fragments—wait, what?

According to YouTuber Smarter Every Day, the tattooing process is simple. Needles take ink and insert it in the skin’s dermis, which is enough layers down to keep it from washing away. As soon as this happens, your body realizes it has been invaded by a foreign contaminate and tries to get rid of the ink by sending in a bunch of white blood cells. However, the metals in the ink are often too large for white blood cells to move. This makes the tattoo permanent and also explains why they fade over time because your body is continually trying to expel it.

With the tattoo firmly implanted in the skin and the ink particles too large to remove, researchers needed a way to break down these large ink patches. Enter, lasers! Lasers, a certain frequency of light, make a lot of heat, especially when they come in contact with a metal. This means that when a laser zaps the heavy metals in ink, the heat causes those metals to break down into smaller pieces.

When the metal is broken down, white blood cells can do their natural job better. In other words, laser tattoo removal isn’t actually removing the tattoo. Instead, it’s making it a lot easier for the body to remove the ink. It also explains why tattoo removal happens in sessions. Basically, the doctor zaps the particles, your body takes them away and the process is repeated until the tattoo is completely gone.

After your white blood cells obtain the ink particles, they take them to your liver, which sends it out of your body when you poop the same way your body gets rid of all of its waste. In essence, the laser only plays a very small role in the whole ordeal because it just aids your body’s natural response to contamination.

Check out Smarter Every Day’s video above to hear about the process more in-depth and to learn about the specific lasers needed to perform the procedure.

(h/t Nerdist via Reddit)