A more serious concern is a blood clot, known as deep vein thrombosis (DVT). This typically causes swelling in one leg along with pain, warmth, or a feeling of tightness. DVT is a medical emergency because the clot can travel to the lungs and become life-threatening.
One-sided leg swelling can also be linked to circulation or lymphatic problems, such as venous insufficiency or lymphedema. If the swelling appears suddenly, worsens quickly, is painful, or is accompanied by chest pain or shortness of breath, medical care should be sought immediately.
