When skin is cut, tiny bodies called blood platelets and proteins such as fibrin rush to the site of the injury, notes Rachel Oswald for HowStuffWorks. They help stop the bleeding, which takes a few minutes, according to MedlinePlus. Later, a scab forms over the wound. The skin then has a protective covering under which to heal.
The body's immune system begins the real work of healing the wound, states MedlinePlus. The wound becomes pink, puffy and oozes a clear fluid to keep itself clean. Blood vessels also open up to get oxygen to the wound, and white blood cells gather to fight infection.
Healing begins at the edges of the wound, explains Oswald. New skin slowly progresses toward the center until the wound is covered. When another layer of skin grows over the wound, the scab drops off. If the wound is shallow, it should not leave a scar. However, if the cut is deep, the body begins a process called cicatrisation, where scar tissue is created from the granular tissue that initially healed the wound. The body produces collagen, a springy material that helps repair an injury that breached the dermis, or the second layer of skin. Cicatrisation takes between three and six weeks; it can two years for the scar to assume its final size and shape.