What is the most common cause of swollen legs?

September 27, 2025 •

3 min read

Swelling in the legs, also known as peripheral edema, is a very common complaint, affecting millions of people in the United States alone. Understanding what is the most common cause of swollen legs is crucial for knowing whether the swelling is a minor issue or a symptom of a more serious underlying health problem.

Quick Summary

The most common cause of swollen legs is chronic venous insufficiency, a condition where leg vein valves weaken and allow blood to pool in the lower extremities. While lifestyle factors can cause temporary swelling, persistent or worsening edema often indicates a more significant health concern requiring medical evaluation.

Key Points

Chronic Venous Insufficiency: The most frequent medical cause of swollen legs is CVI, where weakened vein valves lead to blood pooling in the lower extremities.
Peripheral Edema: This is the medical term for fluid buildup in the legs, ankles, and feet, which is the mechanism behind most cases of swelling.
Serious Medical Conditions: Persistent or severe leg swelling can be a symptom of more serious issues like congestive heart failure, kidney disease, or deep vein thrombosis (DVT), necessitating prompt medical evaluation.
Lifestyle and Medications: Common factors like being overweight, a high-salt diet, prolonged sitting/standing, and certain medications can also cause or worsen leg swelling.
When to Seek Immediate Help: Sudden swelling in one leg with pain, redness, or warmth (potential DVT), or any swelling accompanied by chest pain or shortness of breath, requires emergency medical attention.
Management Strategies: For less severe cases or as part of treatment, elevation, exercise, weight management, reducing salt, and compression stockings can help reduce swelling.

Chronic Venous Insufficiency: The Primary Culprit

Chronic venous insufficiency (CVI) is frequently cited as the most common medical cause of persistent leg swelling, particularly as people age. This condition occurs when the one-way valves in leg veins, responsible for pumping blood back to the heart, become weakened or damaged. As a result, blood can leak backward and pool in the lower legs, leading to pressure and noticeable swelling, medically known as edema.

Risk Factors for CVI

Several factors can increase the likelihood of developing CVI, including increasing age, obesity, pregnancy, and a history of deep vein thrombosis (DVT). Prolonged periods of standing or sitting can also contribute by hindering the calf muscles' ability to assist blood flow.

Other Potential Causes of Leg Swelling

While CVI is common, leg swelling can stem from various other sources, ranging from temporary issues to severe health conditions.

Systemic Conditions

Conditions affecting the body's fluid balance or circulation can cause widespread swelling:

Congestive Heart Failure (CHF): When the heart struggles to pump effectively, fluid can accumulate in the legs.
Kidney Disease: Impaired kidney function leads to excess salt and water retention, often causing swelling in the legs, ankles, and around the eyes.
Liver Disease (Cirrhosis): Severe liver damage can reduce the production of albumin, a protein that helps prevent fluid from leaking into tissues.
Lymphedema: Damage or blockage in the lymphatic system impairs fluid drainage, resulting in swelling, often after cancer treatment.
Hypothyroidism: An underactive thyroid can sometimes contribute to fluid retention.

Other Factors

Medications: Many drugs, including certain blood pressure medications, anti-inflammatory drugs, steroids, and hormones, can cause leg swelling as a side effect.
Injury or Infection: Local trauma like a sprain or fracture causes inflammatory swelling. Skin infections like cellulitis also cause localized swelling, often with redness and warmth.
Dietary Factors: A high intake of sodium can lead to the body retaining excess fluid, causing edema.
Prolonged Immobility: Standing or sitting for extended periods allows gravity to cause temporary fluid pooling in the lower legs.

Key Differences Between Causes

Distinguishing between causes is vital, although medical diagnosis is necessary.


Condition	Typical Presentation	Other Common Symptoms
Chronic Venous Insufficiency	Persistent, gradual swelling (often both legs), worse later in the day.	Heaviness, aching, varicose veins, skin changes.
Congestive Heart Failure	Often bilateral swelling with other significant symptoms.	Shortness of breath, fatigue, weight gain.
Deep Vein Thrombosis	Sudden, usually unilateral swelling with pain and tenderness.	Warmth, redness (a medical emergency).
Lymphedema	Progressive swelling in one or both limbs, feeling heavy.	Aching, thickened skin.
Medication Side Effect	Onset often corresponds with starting a new drug.	Varies by medication.

When to Seek Medical Help

While mild, temporary swelling is often harmless, certain symptoms require prompt medical evaluation. Seek immediate help for sudden, severe swelling in one leg, especially with pain, warmth, or redness, as this could indicate DVT. Swelling accompanied by chest pain, shortness of breath, or dizziness also warrants urgent care, potentially signaling heart failure or pulmonary embolism. Any persistent or worsening swelling should be discussed with a doctor.

Managing Swollen Legs

Treatment focuses on the underlying cause, but general strategies can help:

Elevation: Raising legs above heart level helps drainage.
Movement: Regular physical activity improves circulation.
Compression: Wearing compression stockings can aid blood flow and reduce fluid buildup.
Diet: Reducing sodium intake helps decrease fluid retention.
Medication: Diuretics or adjustments to existing prescriptions may be made by a doctor.

For more information on venous conditions, you can visit the American Heart Association.

Conclusion

While various factors can cause swollen legs, chronic venous insufficiency is the most frequent medical reason for persistent edema. Recognizing the potential causes and knowing when to seek medical attention are essential steps in managing leg swelling and protecting your health.

Frequently Asked Questions

Yes, prolonged periods of sitting or standing are a common cause of temporary leg swelling. Gravity causes fluid to accumulate in the lower extremities. Moving around and elevating your legs can help reduce this type of swelling.

While temporary swelling can occur, you should seek immediate medical attention if you experience sudden swelling in only one leg accompanied by pain, redness, or warmth. This could indicate a deep vein thrombosis (DVT), a medical emergency. Also, see a doctor if swelling is accompanied by chest pain, shortness of breath, or dizziness.

Yes, compression stockings are an effective way to manage swollen legs, especially those caused by chronic venous insufficiency. They apply gentle pressure to the legs, helping to improve blood flow back to the heart and prevent fluid from pooling.

Yes, consuming too much salt can cause your body to retain excess water. This often results in noticeable swelling in the legs, ankles, and feet. Reducing salt intake can help alleviate this.

Yes, leg swelling is a common symptom of congestive heart failure. When the heart's pumping ability is compromised, blood can back up in the veins, leading to fluid accumulation and swelling in the legs.

Mild swelling often refers to temporary fluid buildup from lifestyle factors like standing too long, and it typically resolves on its own. Edema is the medical term for more persistent swelling caused by underlying health conditions like chronic venous insufficiency, heart disease, or kidney problems.

Yes, mild leg swelling is common during pregnancy due to increased blood volume and pressure from the uterus. However, severe or sudden swelling could be a sign of preeclampsia and requires a doctor's attention.