Complex sentence: Type I and Type III collagen comprise 80-85% and 10-15% in uninjured human skin; in the scar over time there is a progressive accumulation of type I collagen and the decline of type III collagen.
Split into simpler sentences: Type I and Type III collagen comprise 80-85% and 10-15% in uninjured human skin. In the scar over time there is a progressive accumulation of type I collagen and the decline of type III collagen.