Why Do We Bruise?
We bruise because the body has received a heavy blow which injures the bodily tissues without rupturing or tearing the outer covering of skin. A bruise is a wound, and a wound may be defined as a breach in the continuity of any body tissue. Often the skin is cut or torn. But closed wounds, such as the rupturing of internal organs, may leave no visible external sign.
A bruise, or contusion of the skin, is caused by the rupture of the blood vessels in the deeper layers of the tissues under the skin. The blood escapes from the damaged vessels into the surrounding tissues and brings about discoloration of the skin, which at first goes red, and then “black and blue”.
As the blood pigments break down, the bruise changes to yellow and green, and eventually fade away. Usually bruises show in the area where the blow has fallen. But there are times when the blood will track along muscles and the planes of connective tissue, causing the bruise to appear some way away from the injury.
As a type of hematoma, a bruise is always caused by internal bleeding into the interstitial tissues which does not break through the skin, usually initiated by blunt trauma, which causes damage through physical compression and deceleration forces. Trauma sufficient to cause bruising can occur from a wide variety of situations including accidents, falls, and surgeries.
Disease states such as insufficient or malfunctioning platelets, other coagulation deficiencies, or vascular disorders, such as venous blockage associated with severe allergies can lead to the formation of purpura which is not to be confused with trauma-related bruising/contusion.
If the trauma is sufficient to break the skin and allow blood to escape the interstitial tissues, the injury is not a bruise but instead a different variety of hemorrhage called bleeding. However, such injuries may be accompanied by bruising elsewhere.
Bruises often induce pain, but small bruises are not normally dangerous alone. Sometimes bruises can be serious, leading to other more life-threatening forms of hematoma, such as when associated with serious injuries, including fractures and more severe internal bleeding.
The likelihood and severity of bruising depends on many factors, including type and healthiness of affected tissues. Minor bruises may be easily recognized in people with light skin color by characteristic blue or purple appearance (idiomatically described as “black and blue”) in the days following the injury.
The presence of bruises may be seen in patients with platelet or coagulation disorders. Unexplained bruising may be a warning sign of child abuse, domestic abuse, or serious medical problems such as leukemia or meningoccocal infection. Unexplained bruising can also indicate internal bleeding or certain types of cancer.
Long-term glucocorticoid therapy can cause easy bruising. Bruising present around the navel (belly button) with severe abdominal pain suggests acute pancreatitis. Connective tissue disorders such as Ehlers-Danlos syndrome may cause relatively easy or spontaneous bruising depending on the severity.