Swelling of the left ankle for no reason and the right foot is normal means that the left ankle joint is swollen while the right ankle joint is normal, and the possible causes are physiological phenomenon, trauma, gout, ankle synovitis and so on. 1. Physiological phenomenon: due to the lack of activity or squeezing of the left lower limb, causing blood circulation in the lower limb is impaired, blood reflux is impeded, resulting in swelling of the left ankle joint, which is a normal phenomenon, and can be relieved on its own. 2. Trauma: The left ankle joint is swollen due to spraining the left ankle joint during exercise or jumping down from a high place, which leads to soft tissue injuries such as muscle and ligament injuries of the left ankle joint or fracture of the heel bone or tibia and fibula, which causes the swelling of the left ankle joint. 3. Gout: Due to long-term consumption of animal offal, seafood and other high-purine foods, urates are deposited in the left ankle joint, causing inflammatory reaction, and swelling of the left ankle joint can occur, mostly accompanied by fever, activity limitation and other symptoms. 4. Ankle synovitis: Synovitis in the left ankle joint due to trauma and excessive exercise can also cause swelling of the left ankle joint. There are many reasons for left ankle swelling but right ankle is normal, it may also be related to left Achilles tendonitis, varicose veins of left lower limb, arterial embolism of left lower limb, osteosarcoma of left lower limb, renal disease, cardiac disease, etc. If the symptom continues to be unrelieved, it is recommended to consult the doctor in time, to clarify the cause of the disease, and then carry out the targeted treatment.