An ecchymosis is the medical term for a subcutaneous purpura

Purpura

Purpura is the appearance of red or purple discolorations on the skin that do not blanch on applying pressure. They are caused by bleeding underneath the skin...

 larger than 1 centimeter or a hematoma

Hematoma

A hematoma, or haematoma, is a localized collection of blood outside the blood vessels, usually in liquid form within the tissue. This distinguishes it from an ecchymosis, which is the spread of blood under the skin in a thin layer, commonly called a bruise...

, commonly called a bruise

Bruise

A bruise, also called a contusion, is a type of relatively minor hematoma of tissue in which capillaries and sometimes venules are damaged by trauma, allowing blood to seep into the surrounding interstitial tissues. Bruises can involve capillaries at the level of skin, subcutaneous tissue, muscle,...

. It can be located in the skin or in a mucous membrane

Mucous membrane

The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...

.

Presentation

After local trauma, red blood cells are phagocytosed and degraded by macrophages. The blue-red color is produced by the enzymatic conversion of hemoglobin

Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

 into bilirubin

Bilirubin

Bilirubin is the yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases...

, which is more blue-green. The bilirubin is then converted into hemosiderin

Hemosiderin

thumb|Hemosiderin image of a kidney viewed under a microscope. The brown areas represent hemosiderinHemosiderin or haemosiderin is an iron-storage complex. It is always found within cells and appears to be a complex of ferritin, denatured ferritin and other material...

, a golden brown color, which accounts for the color changes of the bruise.

Hematomas can be subdivided by size. By definition, ecchymoses are 1 to 2 cm in size or larger, and are therefore larger than petechia (1–2 mm) or pigmented purpuric dermatosis (>3 mm). Hematomas also have a more diffuse border than other purpura.

Generally speaking, dermatologists prefer to differentiate between purpurae

Purpura

Purpura is the appearance of red or purple discolorations on the skin that do not blanch on applying pressure. They are caused by bleeding underneath the skin...

, petechiae

Petechia

A petechia is a small red or purple spot on the body, caused by a minor hemorrhage ."Petechiae" refers to one of the three major classes of purpuric skin conditions. Purpuric eruptions are classified by size into three broad categories...

, and ecchymoses as descriptive technical terms. Other specialties such as internal medicine will frequently call all of these ecchymoses, because the finer distinction is not relevant in the particular case.

See also

• purpura
  Purpura
  Purpura is the appearance of red or purple discolorations on the skin that do not blanch on applying pressure. They are caused by bleeding underneath the skin...
  
  
• Solar purpura
  Solar purpura
  Solar purpura is a skin condition characterized by large, sharply outlined, 1- to 5-cm, dark purplish-red ecchymoses appearing on the dorsa of the forearms and less often the hands....
  
  
• pigmented purpuric dermatosis
• petechia