Ecchymosis is that the medical term for the common bruise. Most bruises form when blood vessels near the surface of the skin are damaged, usually by impact from an injury. The force of the impact causes your blood vessels to burst open and leak blood.
This blood gets cornered at a lower place the skin, where it forms into a little pool that turns your skin purple, black, or blue.
After a blood vessel is injured, platelets in the blood come to help the clotting process. Clotting prevents the injured blood vessels from leaking any more blood and making your bruise even bigger. Some proteins in your blood, called clotting factors, also help to stop the bleeding so that the tissue starts healing.