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?

Question

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:

Answer 1

Unfortunately that piece of information is wrong. All human cells do not replace themselves every 7 years, otherwise we won’t have diseases like Alzheimer’s which are caused by neurons getting damaged over time. Some cell types can replace themselves, such as skin, some can’t, like neurons.

Specific to scarring, the cells that heal the damaged area are not skin, but rather from fibrous tissue. Because of this, even after the scar heals, it remains that way, and future injuries and healings to the scar may also not make it go away.

Ref: https://en.m.wikipedia.org/wiki/Scar

Edit: replaced neurodegenerative with “neurons getting damaged over time” to make it Eli5 compatible

Edit 2: broke the single sentence second paragraph into two sentences for readability