Ecchymosis is the medical term for a bruise over one centimeter in diameter. Smaller bruises may be classified as purpura if they are at least three millimeters in diameter, or petechia if they are smaller. Ecchymosis can appear on the skin or on mucous membranes.
A bruise is a type of hematoma, or a collection of blood outside the blood vessels. It is relatively minor internal bleeding, usually due to blunt force trauma that causes small blood vessels to break under the surface of the skin. Ecchymosis and other bruises are visible when they occur on the skin as a dark spot. Ecchymosis has a more diffuse border than smaller bruises.
In those with light skin color, bruises typically appear purple or blue a few days after injury, then turn green, yellow, and brown as they heal. This gradual change in color is a result of enzymes present in the hematoma during healing. After capillaries or venules break due to local trauma, blood spills into the surrounding area.
Macrophages, white blood cells responsible for cleaning up debris, ingest the red blood cells leaked into the area of the bruise. Through this process, the hemoglobin in the red blood cells is degraded into biliverdin, then bilirubin, then hemosiderin. These different byproducts of the breakdown of hemoglobin are responsible for the changing colors of the ecchymosis. The bruise will not clear until the breakdown process is complete. Often, however, the underlying tissue damage caused by the trauma has been healed well before the breakdown of hemoglobin is complete and the bruise disappears.
Ecchymosis can be treated at home by rest, the application of ice, elevation, and over the counter painkillers. Later in the healing process, light stretching exercises, heat, or light massage may be helpful as long as they do not exaccerbate any pain. If the bruise does not improve after a few days or is extremely painful, or if bruising is frequent, it is important to consult a physician.