If they say that all human cells replace themselves every 7 years or so, why can scars remain on your body for the entire life?
In:
because scar tissue is not the same *type* of tissue as surrounding tissue. So even if the scar tissue is replaced, it’s replaced with the tissue making it up, which does not look the same as the other tissue around it.
For example if you get a small cut the tissue on either side of the cut divides and meets in the middle to repair the cut.
With a larger cut, it might take too long to do this – we need it closed ASAP. So you have tissue from the sides coming together but *also* tissue coming up from below in the middle and all three meet. But now the middle looks like the “below” tissue because that’s what it’s made from
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