Definition [BT: contusion=bruise]
A contusion is an injury to any organ of the body that does not involve a break in the skin. Contusions result when small blood vessels (capillaries) are broken. A collection of blood (hematoma) results when there is a hole or small break in a vein. A superficial contusion has bleeding into the skin or just below the skin (subcutaneous tissue) that is initially visible as a black-and-blue mark. This mark changes colors in a few days to brown, green, and yellow and then fades.
Contusions are usually caused by a fall or direct blow from a blunt object. They are classified as mild, moderate, or severe. If the contusion is superficial, it involves only the skin and subcutaneous tissue. If deep, the muscle and bone may also be involved. Blood can accumulate and form a hematoma within the muscle.
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Treatment
Superficial contusions usually do not require medical attention and are seldom disabling. Ice should be immediately applied to the injury for the first day. This may stop the bleeding and limit the size of the contusion. After 24 to 48 hours, application of heat may help speed resorption of the blood and can be applied in the form of hot soaks, hot showers, heating pads, heat lamps, heat liniments or ointments, or a hot whirlpool bath. Painkillers (analgesics) are administered for pain.
Unexpected bruising, bruising that doesn't have identifiable cause or lingers longer than expected, or bruising without swelling and pain would possbly be best looked at by a GP, in my opinion, just to be safe.
BigTrancer