What Causes Bruising?
Bleeding Under the Skin is Mainly but Not Always Caused by Trauma
Mar 23, 2009
There are a number of conditions which bring about spontaneous bruising and these are mostly related to defects in the body's clotting systems.
A bruise, sometimes known as a contusion, is the result of bleeding under the skin. Bleeding within the skin results in small purplish spots, sort of mini bruises, known as purpura. A raised bruise from a large collection of blood under the skin is called a haematoma.
Other than trauma there are three main reasons for bruising and purpura to occur: fragile or damaged capillaries, lack of platelets and clotting factor problems. In general, problems with capillaries and platelets cause purpura and clotting factor disturbances tend to produce bruises.
Fragile and Damaged Capillaries
There are a few rare inherited conditions in which the capillaries are fragile due to defects in their make up.
The most common reasons for bruising and purpura are either that some people just bruise easily for no apparent reason and in the elderly where the blood vessels are not as robust as before. Some drugs such as penicillin and steroids can weaken the skin and capillaries.
Infections, lupus and rheumatoid arthritis and a number of other diseases, particularly autoimmune varieties, can cause inflammation in the capillaries and lead to bleeding. Henoch-Schonlein purpura is caused by an autoimmune reaction, usually in children and precipitated by infection or medication.
Platelet Deficiency
Thrombocytopaenia means a lack of platelets in the blood. These small cells are made in the bone marrow and are released into the blood stream. They are central to the clotting process: platelets are drawn to areas of tissue damage by chemical messengers. When they arrive at the site they form clumps to plug the hole in the blood vessel thereby preventing further blood loss. This process also triggers the clotting mechanism to form a clot of blood over the damaged area.
Platelet deficiency can be brought about in three ways. Decreased production, excessive platelet destruction and increased consumption of platelets.
- Decreased production by the bone marrow: some types of cancer, leukaemia for example, interfere with bone marrow function. Aplastic anaemia which can be caused by drugs, chemicals, radiation and alcohol involves the destruction of bone marrow. Viral infections can impair the platelet producing ability of the bone marrow.
- Increased platelet destruction: all cells in the body are constantly being destroyed and replaced. If the destruction is too rapid however production of new cells cannot keep pace. Autoimmune illnesses, some drugs, viruses and cancers can bring this situation about.
- Increased use of platelets: occurs when the body's need for platelets outstrips the production rate. This can happen with large blood transfusions, cardiac bypass surgery, artificial kidney dialysis and diseases which cause large numbers of clots in small blood vessels, some liver disorders for example.
Clotting Factor Problems
The clotting process is complex and involves a large number of factors – basically biologically active chemicals that interact with each other to produce a blood clot. Some of these factors are deficient in individuals with inherited clotting disorders. The best known of these are haemophilia A (factor VIII deficiency) and haemophilia B also known as Christmas disease. (factor IX deficiency). People with severe versions of these disorders can experience bleeding into joints as well as bruising.
Some acquired conditions can also disrupt the clotting mechanism including liver disease, pregnancy and certain cancers. Vitamin K is a necessary component of the clotting process so deficiency of this vitamin can cause bleeding. Warfarin, the anticoagulant given to prevent thrombosis, works by interfering with the functioning of vitamin K.
This article is for information only. If you have any health concerns you should consult your doctor.
Resources
Medicine. Eds. Moxham and Souhami. Pub. Churchill Livingstone 2003
Tutorials in Differential Diagnosis. Beck, Francis and Souhami. Pub. Elsevier 2003
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