How does a cut heal? Any cut or scrape that breaks the skin is a wound. A wound heals in stages that overlap. First the leak is stopped. Then germs and debris are cleared, new tissue is built, and the repair is strengthened. Each stage helps the next one.

White blood cells are tiny parts of your blood that fight germs in a wound. They also begin to repair it. They arrive early, soon after the skin is hurt, and they keep working while the cut mends.

Platelets are tiny parts of blood that gather at an injury and help form a clot, which works like a natural bandage. A scab is a dried clot, and it forms within seconds or minutes after the skin is hurt. It acts like a little shield that helps keep germs out of the cut.

In the first few days a cut can be swollen, red and sore. This is the immune system protecting the wound. The swelling and redness are signs that your body is working. A clear or pale yellow fluid may seep from a healing wound, and it helps clean it.

Under a scab, the body repairs broken blood vessels and grows new tissue over about three weeks. New skin cells appear underneath the scab, and the scab stays in place until they do. Collagen is a tough, white protein fiber that the body makes to join the edges of the wound.

Your skin keeps germs out of your body, so when it is cut, wash your hands first. Then wash the cut with mild soap and water soon after it happens. Tell a grown-up. Then cover the cut with a bandage, which keeps it clean while it heals. Even small cuts and scrapes need to be cleaned and covered so they do not get infected.

A scab can itch while the skin under it heals. Scratching it can break the new skin, and picking a scab makes a cut heal more slowly. So it is best to leave the scab alone and let it do its job.

Deep, large or dirty cuts need more care than small clean ones, and a doctor may need to look at them. Yellow or green pus under a scab, spreading redness, more pain or swelling are signs of infection. A grown-up should call a doctor.

When the skin underneath has healed, the scab falls off by itself. Small cuts heal faster than big, deep ones, and young bodies heal faster than older ones. Most small cuts start to heal within a few days.

Words to know

• platelets: tiny blood parts
• collagen: a tough fiber
• immune: germ-fighting
• tissue: body material
• infection: a germ problem

The short version

A scab is a dried clot that forms within seconds or minutes after the skin is hurt. Under it, the body repairs blood vessels and grows new tissue over about three weeks. A wound heals in stages that overlap: the leak is stopped, germs are cleared, new tissue is built, and the repair is strengthened.

Quick facts

• A scab is a dried clot, formed within seconds or minutes of an injury.
• Platelets gather at an injury and help form the clot that works like a natural bandage.
• Under a scab, the body repairs vessels and grows new tissue over about three weeks.
• Collagen is a tough protein fiber that joins the edges of a wound.
• Yellow or green pus under a scab is a sign of infection.