system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If my skin is constantly replacing itself, how do things like scars, moles and tattoos remain permanent?
gpt
Those things all remain for different reasons.

For a scar: Think of your skin like a weave of cloth. Some fibers go - and others go |.  When you get a large enough break in your skin (depth) the fibers will reach across to knit back together. But, all that new skin is basically going in the same direction, rather than in the weave. When they do that, all is well with the world and your skin doesn't really try to get it go be perfect. It's good enough, which means biologically there is no reason for excess resources to be spent "fixing" it. 

For a tattoo, the ink is below the layer that is making your epidermis, but above the other layers. So, skin above is constantly pushing out, but the ink is just a wee bit too deep to get pushed out with it. Tattoos do fade over time, slowly. 

Moles are often much more complex than just areas of skin. Then can be, and often are, malignant melanocytes, basically the thing that makes the melanin (color stuff) in your skin. Your skin wouldn't "know" to cover it or destroy it, as it is skin tissue that is just not doing its job the right way.