Swollen legs result from excess fluid building up in the tissues beneath your skin. The underlying cause can range from something as simple as sitting too long to serious conditions involving your heart, kidneys, or liver. Whether one leg or both are swollen is one of the most important clues to figuring out what’s going on.
Why Fluid Leaks Into Your Legs
Your body constantly moves fluid between your bloodstream and surrounding tissues. Two main forces keep this exchange balanced: the pressure of blood pushing fluid out through tiny blood vessel walls, and proteins in your blood (especially one called albumin) pulling fluid back in. When either of these forces shifts, fluid escapes into the tissue faster than it can be reabsorbed. Gravity pulls that excess fluid downward, which is why legs and ankles are usually the first place swelling shows up.
Anything that raises blood pressure inside your veins, lowers protein levels in your blood, damages blood vessel walls, or blocks your lymphatic drainage system can tip this balance and cause swelling. The specific cause determines whether the swelling appears in one leg or both, whether it’s painful or painless, and how quickly it develops.
One Leg vs. Both Legs: What It Tells You
Swelling in just one leg usually points to a local problem in that limb: a blood clot, an injury, an infection, or a vein that isn’t working properly. Swelling in both legs is more likely tied to a whole-body condition like heart failure, kidney disease, or liver disease. This distinction isn’t absolute. You can have asymmetric swelling from a systemic cause, or a local problem on top of an underlying condition. But the pattern helps narrow things down considerably.
Swelling limited to the calf area is more suspicious for a blood clot or muscle injury, while swelling that involves the entire leg or both legs suggests something happening higher up in the body or a systemic process.
Chronic Venous Insufficiency
One of the most common causes of leg swelling is chronic venous insufficiency (CVI), which affects an estimated 5% to 30% of adults. Veins in your legs contain one-way valves that push blood upward toward the heart. When these valves weaken or fail, blood flows backward and pools in the lower legs. This raises pressure inside the veins, forcing fluid out into the surrounding tissue.
Over time, CVI causes more than just swelling. You may notice varicose veins, skin discoloration (often a brownish or reddish tinge around the ankles), aching or heaviness after standing, and in advanced cases, open sores on the lower legs that are slow to heal. The condition tends to worsen gradually over months and years, and it’s often unequal between the two legs even when both are affected.
Heart, Kidney, and Liver Disease
When the heart can’t pump blood efficiently, blood backs up in the veins. This raises pressure throughout the venous system, and fluid gets pushed out into the tissues of both legs. Heart failure also triggers a chain reaction in the kidneys: sensing reduced blood flow, the body holds onto extra sodium and water to try to compensate, which only adds to the fluid overload. You may notice the swelling worsens over the course of the day and improves somewhat overnight.
Kidney disease causes swelling through a different route. Damaged kidneys can leak protein into the urine, lowering the concentration of albumin in your blood. Since albumin is the main protein responsible for pulling fluid back into blood vessels, losing it means fluid stays trapped in the tissues. The kidneys may also retain sodium and water directly, compounding the problem.
Liver disease, particularly cirrhosis, causes swelling because the liver produces most of the albumin in your blood. A failing liver makes less albumin, reducing the pull that keeps fluid inside blood vessels. Portal hypertension, the buildup of pressure in veins around the liver, adds further strain. Like heart failure, cirrhosis triggers the kidneys to retain extra sodium and water through the same hormonal pathways. The result is often swelling in both the legs and the abdomen.
Blood Clots (DVT)
A deep vein thrombosis, or DVT, is a blood clot that forms in a deep vein, most often in one leg. It typically causes swelling, pain or cramping (often starting in the calf), warmth in the affected leg, and a change in skin color to red or purple. DVT usually affects only one leg, and the swelling can come on over hours to days.
The danger with DVT isn’t just the swelling itself. A clot can break loose and travel to the lungs, causing a pulmonary embolism. Warning signs of this complication include sudden shortness of breath, chest pain that worsens with deep breathing or coughing, a rapid pulse, dizziness or fainting, and coughing up blood. This is a medical emergency.
Risk factors for DVT include prolonged immobility (long flights, bed rest after surgery), recent surgery, cancer, pregnancy, birth control pills or hormone therapy, and a personal or family history of blood clots.
Lymphedema
Your lymphatic system is a separate drainage network that clears fluid and waste products from tissues. When lymphatic vessels are damaged or blocked, fluid accumulates and causes a distinctive type of swelling called lymphedema. This can happen after surgery (especially cancer surgery that removes lymph nodes), radiation therapy, infection, or as an inherited condition.
Lymphedema progresses through four stages. In the earliest stage, the limb looks normal but lymph drainage is already impaired. Stage 1 produces swelling that improves when you elevate the leg. By stage 2, the swelling no longer goes away with elevation, and you can press a dent into the skin. Stage 3 involves significant tissue changes, with thickened skin and fatty deposits that make the limb feel firm rather than spongy.
One useful sign: if you can’t pinch a fold of skin on the top of your foot between your fingers (known as a positive Stemmer sign), lymphedema is likely. This test isn’t perfect. A negative result doesn’t rule it out, especially in early stages. But a positive result is a strong indicator.
Lipedema
Lipedema is an often-misdiagnosed condition involving abnormal fat deposits, almost always in both legs. It looks like swelling, but it’s actually a disorder of fat distribution. Key features that distinguish it from other causes: it nearly always spares the feet (creating a “cuff” effect at the ankles), the legs are disproportionately painful and tender to touch, and you bruise unusually easily. Lipedema predominantly affects women, often begins or worsens during hormonal shifts like puberty or pregnancy, and doesn’t improve with weight loss or elevation.
Medications That Cause Swelling
Several common medications can cause fluid retention and leg swelling as a side effect. Calcium channel blockers (a type of blood pressure medication) are among the most frequent culprits. Others include certain diabetes medications, anti-inflammatory drugs like ibuprofen and naproxen, steroids, and some hormonal treatments including estrogen and testosterone. If your leg swelling started shortly after beginning a new medication, that connection is worth investigating with whoever prescribed it.
Pregnancy-Related Swelling
Some degree of leg swelling is normal during pregnancy. The growing uterus puts pressure on the large veins that return blood from the legs, blood volume increases substantially, and hormonal changes make blood vessel walls more permeable. Most pregnancy-related swelling is harmless and concentrated in the ankles and feet, especially later in the day.
What isn’t normal is sudden, severe swelling, particularly in the face and hands. This can be a sign of preeclampsia, a serious pregnancy complication defined by high blood pressure and signs of organ damage. Other warning signs include severe headaches, vision changes (blurred vision, light sensitivity, or temporary vision loss), upper belly pain on the right side, shortness of breath, and nausea or vomiting that appears in the second half of pregnancy. Preeclampsia requires prompt medical attention.
Lifestyle Factors and Sodium
Not all leg swelling signals a medical condition. Prolonged sitting or standing, especially in warm weather, causes fluid to pool in the legs simply due to gravity. Long flights and car rides are classic triggers. Obesity increases pressure on the veins returning blood from the legs, making swelling more likely. A sedentary lifestyle reduces the muscle pumping action in your calves that normally helps push blood upward.
Sodium plays a significant role. High sodium intake causes your body to retain water, increasing fluid volume throughout your system. For people prone to edema, a stricter sodium limit of 1,375 to 1,800 mg per day is generally recommended, well below the average intake of over 3,400 mg per day in the United States. Reading labels matters here, since processed foods, restaurant meals, and even bread can contain surprisingly high amounts.
Elevating your legs above heart level for 20 to 30 minutes several times a day helps fluid drain back toward the center of your body. Compression stockings apply graduated pressure that supports your veins and reduces pooling. Regular walking activates the calf muscles that act as a pump for venous blood. These strategies help manage swelling from many causes, though they won’t resolve swelling driven by a serious underlying condition on their own.
What Pitting Edema Means
If you press your thumb firmly into your swollen shin for a few seconds and it leaves an indentation that slowly fills back in, that’s called pitting edema. Clinicians grade this on a scale from 1+ (a shallow dent less than 4 mm deep) to 4+ (a deep dent of 8 mm or more). Pitting edema is typical of fluid-related swelling from heart, kidney, liver, or venous causes. Non-pitting swelling, where the skin springs back immediately, is more common in lymphedema and lipedema, where the tissue composition has changed beyond simple fluid accumulation.
The depth and persistence of pitting give a rough sense of severity, but they don’t tell you the cause. Mild pitting in your ankles at the end of a long day on your feet is common and usually benign. Pitting that extends up to the knees, is present first thing in the morning, or worsens over weeks warrants medical evaluation to identify what’s driving it.