A bruise (ecchymosis or haematoma in medical jargon) occurs when part of the body is struck by a blunt object to cause rupture of blood vessels under the skin or when internal structures rupture blood vessels by their movement (e.g. a fracture of a bone). Blood vessels can also rupture by stretching when a joint is overextended (e.g. a severe sprain) or if blood fails to clot rapidly when a blood vessel receives minor damage.
If an artery ruptures a bruise will form immediately, with swelling and a blue/black tinge to the overlying skin. A bruise develops more slowly and with less swelling if a vein ruptures. It is far harder to rupture an artery which has a muscular thick wall than a vein, which normally has a much thinner wall. Blood under pressure can track its way between layers of tissue so that bruising may occur, not only at the site of the injury, but some distance away (e.g. a kick to the calf may cause a spot bruise on the calf, but a day or two later bruising may appear around the ankle).
Patients on medication (e.g. warfarin) which is prescribed to reduce the speed at which blood clots form (to prevent strokes or heart attacks) will bruise far more easily than normal people. Aspirin, anti-inflammatory medications (for arthritis) and other less commonly used drugs may also increase bleeding and therefore bruising.
Women bruise more easily than men, particularly around the menopause, because hormonal changes may make blood vessel walls weaker, allowing them to rupture easily. Many women complain of multiple small bruises on their arms and legs, in places where they cannot recall any significant injury.
Other common causes of abnormal bruising include thrombocytopenia (a lack of platelets in the blood), Cushing syndrome (over production of steroids in the body, or taking large doses of cortisone) and leukaemia (cancer of the white blood cells).
When a bruise is likely or first develops after an injury, try to reduce the blood flow to the area. The affected area should be cooled with ice, elevated and rested. The ice should not be applied directly to the skin, but wrapped inside a cloth. Elevation of the area reduces the pressure in the veins and slows blood loss from the ruptured blood vessel. Any exercise or movement involving an area with a ruptured blood vessel will force more blood out into the tissues.
With time and rest the swelling will reduce, the bruise will go from blue/black to purple, then brown and finally yellow before disappearing. There may be some residual swelling and firmness at the bruise site due to the formation of fibrous scar tissue and the skin over the area may dry out and flake off.
If there is no apparent cause for a bruise, medical advice should be sought.