How do scabs form?

Whether it’s skinning your knee or scraping your arm, injuries that break skin can be painfully memorable. But what may go unnoticed is the body’s healing response. This four-stage process is aided in large part by scabs, the rough and crusted blood clots that protect wounds and promote their healing. Scabs are formed during the first step of wound healing. Immediately after skin is broken, platelets and some other cells from the blood form a clot to minimize bleeding. This combination of cells begin to clump and are held together by a protein called fibrin, which forms a fibrous net to hold the clot in place. The clot dries and hardens to form a scab, which seals and protects the wound in the next phases of healing. The second stage increases blood flow to the wound, bringing oxygen, nutrients, and other cells to fight infection and repair the wound. In the third stage, collagen and elastin serve as a scaffolding for new tissue to begin forming underneath the scab. The two proteins form a scar, which eventually lightens and strengthens in the final phase of the healing process. As scar tissue forms, the scab will eventually fall off—after a couple of days or weeks, depending on the size of the wound. Scabs often itch as they heal, a sensation that may be caused by histamines, cytokines, and other substances that cause and control inflammation. But as tempting as it may be, avoiding the urge to scratch the scab is important to the healing process. Scratching may reopen the wound, potentially leading to further scarring and even infection.