system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If all of the cells in our bodies are replaced within a matter of years, how are tattoos permanent?
gpt
Imagine a bucket filled with ping pong balls. That's your skin. The ping pong balls are your skin cells. Now imagine filling the bucket with some water. That's the tattoo ink.  You can replace any or all of those balls, and they might take some water with them, but that water is pretty much going to stay in the bucket.