One leg swelling below the knee: what to know

A clot in a deep vein may cause swelling, tightness or pain in the calf, sometimes with warmth or redness. A muscle strain, soft-tissue injury, joint inflammation, skin infection or a blocked lymph channel can look similar. Varicose veins may cause aching and swelling that becomes more noticeable after standing; see [Varicose Veins](/conditions/varicose-veins/) for background. Conditions that cause fluid retention, such as [Heart Failure](/conditions/heart-failure/) or [Chronic Kidney Disease](/conditions/chronic-kidney-disease/), commonly affect both legs rather than only one.

A clinician may compare the leg circumference and skin, check pulses and tenderness, and arrange an ultrasound if a clot is a concern. Do not try to diagnose the cause by pressing the calf.

Arrange same-day medical advice for new or unexplained one-sided swelling, particularly after travel, an operation, prolonged bed rest, pregnancy, or if you have had a clot before. Note when it started, whether the swelling reaches the ankle or thigh, and whether there is pain, heat, redness or breathlessness. Avoid vigorous exercise and leg massage until assessed. Keep the leg comfortable and take only medicines recommended for you. General terms are explained on [Swollen Ankles](/symptoms/swollen-ankles/).

Use emergency services for sudden breathing difficulty, chest pain, coughing blood, collapse, faintness or a very fast heartbeat. Seek urgent care today if swelling is rapidly worsening, the calf becomes hot and painful, or redness spreads with fever. A cold, pale or blue foot, new numbness, or severe pain also needs immediate assessment.

Ask what causes are most plausible from your history, whether an ultrasound is needed, whether you should limit activity, and which symptoms require emergency help. Also ask how to monitor the swelling and when to arrange follow-up if the test is reassuring.