What causes swelling in the leg?

September 27, 2025 •

5 min read

According to the National Institutes of Health, fluid retention is one of the most common reasons for leg swelling, affecting millions of adults. Understanding what causes swelling in the leg is crucial, as it can range from temporary, harmless issues to serious, chronic health conditions requiring medical attention. This guide will walk you through the various culprits behind swollen legs, so you know when to seek help.

Quick Summary

Swelling in the leg, also known as edema, is caused by fluid buildup or inflammation from factors including lifestyle habits, venous insufficiency, deep vein thrombosis, and organ diseases affecting the heart, liver, or kidneys. Addressing the root cause, with medical guidance for severe cases, is key to managing this common condition.

Key Points

Diverse Origins: Swelling in the leg (edema) can be caused by a wide range of factors, including lifestyle habits like prolonged sitting, medical conditions such as heart or kidney failure, venous insufficiency, and localized issues like infections or injuries.
Unilateral vs. Bilateral: Swelling in one leg (unilateral) often indicates a localized problem like a blood clot (DVT) or infection, while swelling in both legs (bilateral) is more commonly associated with systemic issues affecting the whole body, such as heart disease.
Serious Conditions: Urgent medical attention is required for sudden, unexplained leg swelling, especially if accompanied by chest pain, shortness of breath, dizziness, or a fever, as it could indicate a dangerous blood clot (DVT) or heart condition.
Effective Home Remedies: For mild, non-emergency swelling, simple remedies like elevating the legs, regular movement, reducing salt intake, and wearing compression stockings can help manage symptoms.
Medication Side Effects: Certain medications, including some blood pressure pills and NSAIDs, can cause fluid retention leading to leg swelling. Always consult a doctor before altering your medication regimen.
Lifestyle Management: Maintaining a healthy weight and staying active can significantly reduce pressure on your circulatory system and prevent fluid accumulation in the legs.

Understanding Edema and How It Develops

Swelling in the leg, medically referred to as peripheral edema, occurs when fluid from your blood vessels leaks into the surrounding tissues. Gravity naturally pulls this fluid downwards, making the feet, ankles, and legs the most common areas to experience swelling. While temporary swelling after a long day of standing is normal, persistent or severe edema can signal a more significant health problem.

There are two main types of leg swelling: unilateral (one leg) and bilateral (both legs). Swelling in only one leg often points to a localized issue, like an infection or blood clot, while swelling in both legs is more indicative of a systemic condition affecting your entire body, such as heart failure or kidney disease.

Medical Causes of Leg Swelling

Numerous medical conditions can lead to swelling in one or both legs. Understanding these is the first step toward proper diagnosis and treatment.

Cardiovascular Conditions

Chronic Venous Insufficiency (CVI): This is one of the most frequent causes of leg swelling. In CVI, the valves in the leg veins are damaged or weakened, preventing blood from flowing efficiently back to the heart. This causes blood to pool in the lower legs, leading to swelling, pain, skin discoloration, and varicose veins.
Heart Failure: When the heart's pumping ability is compromised, fluid can back up into the veins, leading to fluid accumulation in the legs and abdomen. Swelling from heart failure is typically bilateral and accompanied by other symptoms like shortness of breath and fatigue.
Deep Vein Thrombosis (DVT): This is a serious condition where a blood clot forms in a deep vein, usually in the leg. DVT typically causes sudden, painful swelling in just one leg and requires immediate medical attention to prevent the clot from traveling to the lungs, a condition known as a pulmonary embolism.

Organ-Related Diseases

Kidney Disease: The kidneys are responsible for regulating fluid and mineral balance in the body. When kidney function is impaired, excess fluid and sodium can build up, resulting in widespread edema, particularly in the legs.
Liver Disease: Severe liver disease, or cirrhosis, can lead to swelling for two main reasons. The diseased liver fails to produce enough albumin, a protein that keeps fluid in the bloodstream. Additionally, liver disease can increase pressure in the veins carrying blood from the lower body to the liver, causing fluid to pool in the legs and abdomen.

Lymphatic System Issues

Lymphedema: This occurs when a blockage or damage to the lymphatic system prevents lymphatic fluid from draining properly. The fluid then builds up in the tissues, causing swelling that can be either congenital or acquired, often after surgery or radiation treatment for cancer involving lymph node removal. Lymphedema can affect one or both legs and sometimes results in non-pitting edema.

Other Inflammatory and Traumatic Causes

Infection: Localized swelling can be the result of a bacterial infection, such as cellulitis, which affects the skin and underlying tissues. This swelling is often accompanied by pain, redness, and warmth.
Injury: Sprains, fractures, or other trauma to the leg or ankle can cause swelling as a natural inflammatory response.
Arthritis: Inflammatory joint conditions like rheumatoid arthritis or osteoarthritis can cause localized swelling around the affected joints.

Lifestyle and Medication-Induced Swelling

Sometimes, leg swelling is a side effect of daily habits or medications.

Common Lifestyle Factors

Prolonged Sitting or Standing: Staying in one position for long periods, especially during travel or a sedentary job, allows fluid to pool in the lower extremities due to gravity.
Excess Sodium Intake: A high-salt diet can cause the body to retain excess water, contributing to swelling.
Obesity: Excess body weight increases pressure on the veins and lymphatic vessels, hindering proper fluid return and contributing to edema.
Pregnancy: Many pregnant women experience swelling in their legs, ankles, and feet due to increased blood volume and pressure from the growing uterus on pelvic veins.

Medications That Can Cause Swelling

Some common medications list leg swelling as a potential side effect. These include:

Non-steroidal anti-inflammatory drugs (NSAIDs)
Calcium channel blockers for high blood pressure
Hormone replacement therapy and birth control pills
Certain antidepressants and diabetes medications

It is important to never stop taking a prescribed medication without first consulting your doctor.

Comparison of Swelling Causes

To help differentiate between potential causes, this table compares some key characteristics.


Feature	Chronic Venous Insufficiency (CVI)	Deep Vein Thrombosis (DVT)	Heart Failure	Lymphedema
Onset	Gradual, worsens over time	Sudden, often without clear cause	Gradual, with other systemic symptoms	Can be slow or sudden, often post-surgery
Location	Typically both legs, can be unequal	Usually one leg only	Usually both legs equally	One or both legs
Appearance	Pitting edema, skin changes	Pitting edema, redness, warmth	Pitting edema	Non-pitting edema
Associated Symptoms	Varicose veins, skin ulcers	Pain, tenderness, fever	Shortness of breath, fatigue	Feeling of heaviness
Urgency	Seek routine medical care	Immediate medical attention	Immediate medical attention if severe	Seek routine medical care

When to See a Doctor

While occasional, temporary swelling can be managed with at-home care, certain symptoms require immediate medical attention to rule out serious conditions like DVT or a cardiac issue. Call 911 or seek emergency medical care immediately if leg swelling is accompanied by:

Chest pain or pressure
Difficulty breathing or shortness of breath
Dizziness or fainting
Coughing up blood

Schedule a doctor's visit as soon as possible if you experience:

Sudden or unexplained swelling, especially in only one leg.
Swelling that does not improve with elevation or rest.
Leg pain, redness, or warmth in the swollen area.
Discoloration or shininess of the skin on your leg.

At-Home Remedies and Prevention

For mild, non-emergency swelling, several lifestyle adjustments and home remedies can help alleviate symptoms.

Elevate Your Legs: When resting, place your legs on pillows to raise them above the level of your heart. This uses gravity to help drain fluid.
Move Regularly: Regular exercise, even gentle walking, helps pump fluid from the legs back to the heart. Avoid sitting or standing in one position for too long; take frequent breaks to stretch and move.
Reduce Sodium Intake: A low-salt diet can help minimize fluid retention and reduce swelling.
Wear Compression Stockings: These garments apply pressure to the legs to improve circulation and prevent fluid buildup. They are available at most drugstores.
Stay Hydrated: Drinking plenty of water helps your body maintain a healthy fluid balance, which can reduce swelling.
Manage Your Weight: Maintaining a healthy body weight can reduce the pressure on your leg veins and lymphatic system, improving circulation.

Conclusion

Swelling in the leg can have a wide array of causes, from simple lifestyle factors to serious, underlying medical conditions. While minor swelling can often be managed with home remedies, it is crucial to recognize when symptoms warrant a visit to a doctor. Persistent, sudden, or accompanied by other worrying symptoms, leg swelling should always be evaluated by a healthcare professional to ensure proper diagnosis and treatment. By understanding the potential causes, you can take proactive steps to protect your health and address the issue effectively.

For more in-depth medical information on specific conditions related to edema, consult reputable sources like the Mayo Clinic.

Frequently Asked Questions

The most common causes of swelling in both legs (bilateral edema) include chronic venous insufficiency, heart failure, and kidney or liver disease. Lifestyle factors like obesity or prolonged periods of standing or sitting can also cause bilateral swelling.

Leg swelling is a medical emergency if it appears suddenly and is accompanied by symptoms like chest pain, difficulty breathing, dizziness, or coughing up blood, as these could indicate a serious blood clot in the lungs or a severe heart condition. Seek immediate medical care.

Yes, a high-sodium diet can cause your body to retain water, leading to leg swelling or edema. Reducing your salt intake can help alleviate or prevent fluid retention.

For mild swelling, you can elevate your legs above heart level, exercise gently, wear compression stockings, and reduce salt intake. Avoid standing or sitting for long periods and take regular breaks to move around.

Swelling in only one leg can be more alarming, as it might indicate a localized, serious issue like a deep vein thrombosis (DVT), a blood clot in a deep vein. Swelling in both legs is often due to more widespread, systemic conditions.

Yes, several medications can cause leg swelling as a side effect, including some blood pressure medicines (calcium channel blockers), non-steroidal anti-inflammatory drugs (NSAIDs), and certain hormone therapies. If you suspect a medication is the cause, consult your doctor.

Pitting edema is swelling that leaves a temporary indentation in the skin after pressure is applied, typically caused by fluid buildup from venous or organ issues. Non-pitting edema does not leave an indentation and is often associated with lymphedema.