Swelling of the legs, ankles, or feet — known medically as peripheral oedema — is extremely common and has a wide range of causes, from entirely benign to potentially life-threatening. Understanding the pattern of swelling (which leg, how quickly it developed, whether it pits with pressure, and what accompanies it) helps distinguish conditions requiring emergency evaluation from those needing only simple reassurance or lifestyle changes.
How to Assess Your Swelling
Pitting oedema — pressing a finger against the swollen area leaves an indentation — indicates accumulation of excess fluid in the interstitial space, suggesting a systemic cause (heart failure, kidney disease, liver disease, or medication). Non-pitting oedema results from lymphatic obstruction or inflammatory conditions. Unilateral swelling (one leg only) raises immediate concern for deep vein thrombosis (DVT) or local causes. Bilateral swelling is more commonly systemic or venous insufficiency.
Serious Causes That Need Prompt Evaluation
Deep Vein Thrombosis (DVT)
A blood clot in a deep leg vein typically causes unilateral calf swelling, warmth, redness, and pain — though it can be asymptomatic. DVT is dangerous primarily because of the risk of pulmonary embolism if the clot dislodges and travels to the lungs. Risk factors include prolonged immobility (long flights, bed rest), recent surgery, cancer, oral contraceptives, and pregnancy. Diagnosis requires compression ultrasound; treatment is anticoagulation. Suspect DVT for any unexplained unilateral leg swelling.
Heart Failure
When the right heart cannot adequately manage venous return, fluid backs up into the systemic veins and leaks into tissues. The result is symmetrical, bilateral ankle and leg swelling that worsens throughout the day and improves overnight with leg elevation. It is typically accompanied by dyspnoea, fatigue, and reduced exercise tolerance. Echocardiography diagnoses cardiac dysfunction; treatment with diuretics, ACE inhibitors, and beta-blockers reduces both symptoms and mortality.
Kidney and Liver Disease
Nephrotic syndrome (protein loss through damaged kidneys) and cirrhosis (reduced albumin synthesis by the liver) both reduce plasma oncotic pressure, allowing fluid to leak from blood vessels into tissues. Oedema in these conditions is often generalised — including facial puffiness in the morning — and accompanied by other systemic features.
Common Benign Causes
Chronic Venous Insufficiency
Damaged or incompetent valves in leg veins allow blood to pool in the lower extremities. This produces bilateral ankle swelling that worsens with prolonged standing and improves with leg elevation, often accompanied by varicose veins, skin discolouration (lipodermatosclerosis), or venous ulcers at the ankles. Compression stockings (20–30 mmHg) are the primary management; severe disease may benefit from endovenous laser ablation.
Dependent Oedema
Gravity causes fluid to accumulate in the feet and ankles after prolonged sitting or standing in people with normal hearts and kidneys. It is common in people who sit for long hours, on long flights, or in hot weather. It resolves with elevation and is not associated with cardiovascular disease.
Medications
Calcium channel blockers (amlodipine, nifedipine) — commonly prescribed for hypertension — cause dose-dependent ankle oedema in up to 30% of users. NSAIDs, corticosteroids, and some antidepressants also cause fluid retention. Review medications when new bilateral oedema develops.
Sources
- Cho S, et al. Peripheral Edema. Am J Med. 2002.
- Kearon C, et al. Antithrombotic Therapy for VTE Disease. Chest. 2016.
- Mayo Clinic. Edema — Causes. 2023.