My husbands left foot is consently swelling up ? why is that

Few reasons: A foot can swell, incompetent valves in veins, varicose veins, gravity, high blood pressure, a stress fracture, certain arthridities, side effects of medicine, due to the many possibilities best to see a doc.

Swelling: Most often with one sided extremity swelling is due to old trauma and damage to venous or lymphatic damage. Poor cardiac output can also cause single limb swelling. Should see your cardiologist to rule out heart problems. Then treat with compression socks.

Vascular problem: If just the left foot is swelling up, the most likely causes are a poor circulation the foot, or blood clot to the leg or lymph node blockage, venous problem or some ligament or tendon tear. Please see your podiatrist for a thorough workup for this condition.