DEAR DOCTOR K:
How and why does a scar form after injury or surgery? Why do some scars last, while others fade over time?
It’s actually amazing how few scars most people have despite a lifetime of injuries to the skin.
Skin heals in a remarkably complicated process. When you cut yourself (or a surgeon makes an incision), three processes take place in roughly the following order, although they often overlap:
- Inflammation. When you cut the skin (or any other tissue), the tiny blood vessels inside the skin start bleeding. Within seconds of a cut or an incision, cells near the cut send out chemical signals that tell blood vessels to narrow. This limits bleeding until blood cells (called platelets) can form tiny clots that plug up the ends of the tiny vessels and thereby stop the bleeding.
- Additional chemical signals recruit white blood cells and other substances to the injured area. These white blood cells release a flood of chemical factors to relax blood vessels that were not cut and thereby increase blood flow to the injured area. This causes the pain, redness, heat and swelling typical of inflamed tissue. The white blood cells are part of the immune system. They fight infection and clean up damaged tissue.
- Proliferation. In this stage, cells start to form new blood vessels to replace the ones that were severed by the cut. Skin cells burrow under dead tissue to begin forming a healthy layer of skin. Fibroblasts, specialized cells that are critical to wound healing, produce substances that pull the ends of the wound closer together. The fibroblasts also form a small scar over the injured area, which protects the new skin and blood vessels growing underneath it.
- Maturation. The wound gets stronger.
If the two sides of a wound are too far apart, it will take a long time to repair the cut, and it is more likely to leave a scar. That’s why surgeons use sutures (stitches), staples or tape to bring the edges together when they’ve made a wound.
So why are some scars bigger than others? If a wound is “clean” — even, straight, and not contaminated by dirt and bacteria — it will generally heal well. Wounds caused by a surgeon’s knife fall into that category.
Wounds caused by accidents don’t. Such wounds are more likely to be jagged, to contain dirt and bacteria, and to be infected. These wounds are more likely to have been reinjured or reopened after the initial accident. All of these factors tend to increase the chance of a permanent scar.
Finally, some people are born with a tendency to form prominent scars called “keloids.” These scars do tend to get smaller with time, and there are treatments to make them smaller if they are bothersome.
So we form scars because they help us heal. But our genes, what caused the cut that led to the scar and how the cut was treated all affect a scar’s size and permanence.