Swelling of the left leg requires vigilance against factors such as prolonged standing and lack of activity, as well as trauma to the left lower extremity, deep vein thrombosis, cellulitis and other causes. 1. Physiological factors such as standing on the left leg for a long time or not moving the left leg for a long time lead to stagnation of blood in the veins of the left leg, and thus swelling of the left leg. 2. Traumatic injury: the left leg is swollen after being squeezed, collided, burned, punctured and other traumatic injuries, resulting in damage to the subcutaneous connective tissue or even fracture, and the local exudation increases. 3. Deep vein thrombosis: the deep veins of the left leg form thrombus due to long-term bed rest and other factors, resulting in venous return obstacles in the left leg, and thus the left leg will be swollen. 4. Cellulitis: Swelling of the left leg due to the formation of connective tissue pus cavities in the left leg as a result of a localized suppurative infection. Swelling of the left leg may also have other causes, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.