Patients who always have a bruise on their legs without a history of significant trauma may have idiopathic thrombocytopenic purpura, an acquired bleeding disorder of unknown origin. Patients with idiopathic thrombocytopenic purpura are prone to bleeding, some patients can develop skin mucosal petechiae, commonly on the upper extremities and distal lower extremities, and may also have bleeding gums and nosebleeds. In addition, bruising on the legs may also be caused by hematological diseases, such as aplastic anemia or leukemia, due to thrombocytopenia may also appear skin petechiae. In addition, this condition may also be caused by taking certain drugs, such as some patients often take anti-platelet drugs and anticoagulant drugs, which may cause platelet abnormalities or clotting abnormalities, and thus prone to skin bruising. Therefore, further examination is needed to clarify the diagnosis.