system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are tattoos permanent if every cell in your body is replaced every 7 - 10 years?
gpt
Tattoos are ink injected into/under the skin, so while they're technically 'part of your body', that's only in the sense that a replacement hip is 'part of your body' - tattoo ink isn't on the list of cells that die and are replaced naturally by your body.

They will break down over the years (which is why old tattoos can look 'muddy'), but that's a property of the ink itself breaking down and, again, not part of your body's cell-replacement-action.