One side leg swelling: what should you know?

Swelling may follow an injury, prolonged sitting, infection, vein problems, or a clot in a deep vein. Varicose veins can cause heaviness and swelling that changes through the day. Heart failure or chronic kidney disease can also cause fluid retention, although this more often affects both legs. Obesity can increase pressure on veins and make swelling more noticeable. Compare both legs and note warmth, colour change, tenderness, skin tightness, and whether the swelling leaves a dent after gentle pressure.

If the swelling is mild and follows a clear cause such as a long journey, avoid sitting still for long periods, move your ankle and walk gently if comfortable, and raise the leg when resting. Do not massage a painful, warm, or suddenly swollen leg. Do not start compression socks or water tablets without advice, because the right approach depends on the cause. Arrange a clinical assessment for unexplained swelling, especially if it persists, returns, or affects walking. A clinician may examine the leg and review medicines and health conditions.

Seek emergency help if leg swelling occurs with sudden breathlessness, chest pain, coughing blood, faintness, or a racing heartbeat. Get prompt same-day assessment for sudden swelling, significant calf pain, warmth, redness, or tenderness, particularly after surgery, immobility, long travel, pregnancy, or previous clotting problems. Fever with a red, hot, painful leg also needs urgent review. Call for advice if swelling is rapidly increasing or the foot becomes cold, pale, blue, numb, or severely painful.

Ask what cause is most plausible, whether you need imaging or blood tests, how much activity is safe, and whether compression is appropriate. Mention recent travel, injury, surgery, pregnancy, new medicines, breathlessness, and any history of heart, kidney, or vein disease.