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The cause of spontaneous bruises on the skin, which is not due to trauma, could be due to âbleeding disorders or clotting disorders associated with dysfunction of platelets or the coagulation âsystem. â
In case the bruise has persisted for a long time, it could be due to a large hematoma, within the skin. In such conditions, the collected blood may need a longer time, before the hemosiderin in the blood clot is slowly absorbed by the body.
You might consult with your doctor for a examination and a few blood tests (bleeding time, âcoagulation profile and a complete hemogram) which may give additional information and provide a âproper help.