Watch: The chemistry behind tattoos

Tattoos have been around for thousands of years—but how do they work? According to the American Chemical Society, modern tattoo needles puncture the skin at 50 to 3000 times per minute, going through the epidermis, the outer layer of our skin, into the dermis, the inner layer. Immediately, microphages or white blood cells prompted by the immune system attempt to heal these wounds by gobbling up the “foreign invader.” Yet instead, they get stuck in the “gellike matrix” of the dermis—pretty much forever. That is why the tattoo remains in your skin permanently. However, skin cells in our epidermis live for only 2 to 3 weeks, explaining why tattoos fade with time.

(Video credit: Reactions)