The causes of swelling in the left foot are as follows: 1. Trauma to the left foot, especially trauma that causes significant soft tissue damage, destruction, or fracture, can lead to significant swelling, pain, and limited activity in the left foot. 2. Poor blood circulation in the left lower extremity can also lead to bruising and swelling in the left foot. 3. Degeneration and osteophytes in the left foot can easily lead to swelling in the left foot after activity. 4. Infection in the left foot area may also lead to obvious redness, swelling, heat and pain in the left foot. After the swelling of the left foot occurs, the patient must consult a doctor to see what causes it, and treat the cause to promote the absorption of the swelling of the left foot and to restore the normal force activity of the left foot.