Why don’t tattoos just go away? If it’s just staining your cells and the cells eventually die, wouldn’t it just disappear?
Because the ink is stored in the dermis the deeper layer of skin that doesn’t replenish near as fast, that and the ink is literally passed on to the newly generated cells.
It doesn’t stain your cells. Pigment is injected into the dermis, and it’s basically just chunks of inorganic matter that has a particular color. Part of the tattoo actually breaks down as smaller fragments of pigment are removed by your white blood cells, but the bigger chunks they can’t remove and they stay. Smarter Every Day has a neat [video](https://youtu.be/D0B7F5UbTOQ) that shows how this works, and how a laser tattoo removal breaks down the pigment so your body can do the rest.
Because of your immune system. The ink is eaten by phagocytes as if it was an invading organism. This changes their color, and this is passed down from generation to generation of phagocytes, continuing the process.
The ink goes into a deeper layer of skin than just what’s on the surface, so it holds for much longer. Some colors do fade faster than others, and tattoos on certain parts of the body (like on the palm of the hand or inside of a lip) will not last as long as others.
And they can get faded faster through unprotected exposure to the sun or other sources of UV light.