How does repaired skin become a scar?

A scar forms when damaged skin repairs with tissue that differs from the original. After an injury reaches deeper supporting tissue, the body does more than stop bleeding. It must build material across the damaged area and cover the surface again. These repair processes overlap rather than waiting for separate starting signals.

Cells called fibroblasts help construct the new support. They produce collagen, a strong fibrous protein, along with other material around the cells. New small blood vessels support the growing tissue, while surface cells move and multiply to cover the gap. Collagen helps bridge the injury and strengthen the repair.

The first supporting material is not the final arrangement. During remodeling, some material is broken down and replaced, and collagen fibers are reorganized. The amount and organization of the tissue change as the scar matures. Numbers of some repair cells and small blood vessels also decrease. Its appearance can change as well, often becoming softer, flatter or paler over time.

Repaired skin does not exactly reproduce the structure of skin that was never injured. Collagen can be arranged differently, helping explain the lasting difference in texture or appearance. Scar formation is therefore an ongoing tissue repair process, extending beyond the early blood clot that helped limit bleeding.