system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does the human body differentiate between abrasions and cuts or stretch marks? And if the body sees them similarly, why do they heal differently?
gpt
Not sure what you mean? It depends on the depth/extent of the injury. If the damage reaches to the basement membrane separating the skin from the underlying tissue, the skin can't repair itself properly so it "paves it over" with a bunch of collagen fibers, forming a scar.

A stretch mark is essentially the skin tearing itself from the underlying tissue growing too quickly.