Venous thrombosis is the abnormal clotting of blood in a vein to form a blood clot for some reason. The main causes of venous thrombosis are damage to the vein wall, blood stasis, and hypercoagulability of the blood. Venous thrombosis occurs in the elderly, people with malignant tumors, people who have been bedridden for a long time, women in labor, and people in the late stages of pregnancy. There are three main causes of venous thrombosis: 1. Damage to the vein wall: It is due to the damage to the vein wall which leads to the exposure of collagen and the coagulation of platelets and other substances in the blood vessels. 2. Blood stagnation: The thrombus is formed mainly due to slow blood flow, which causes platelets and other substances to remain in contact with the blood vessel for too long. 3. Hypercoagulability of blood: Venous thrombosis occurs when the body’s anticoagulant mechanism is affected due to surgery, trauma or tumor. After the occurrence of venous thrombosis, you should go to the hospital in time, complete the examination, make a clear diagnosis and then be treated accordingly.