Swollen legs happen when fluid builds up in the tissues of your lower extremities, a condition called peripheral edema. The causes range from sitting too long on a flight to serious conditions like heart failure or blood clots. Most cases involve fluid that leaks out of tiny blood vessels and collects in surrounding tissue, driven by pressure changes, inflammation, or problems with drainage. Understanding the pattern of your swelling, whether it affects one leg or both, and what other symptoms accompany it can point you toward the likely cause.
How Fluid Ends Up in Your Legs
Your body constantly moves fluid between your bloodstream and the tissues around it. Two opposing forces control this exchange: the pressure of blood pushing fluid out through vessel walls, and proteins in your blood pulling fluid back in. When something disrupts this balance, fluid escapes faster than your body can reabsorb it. Gravity pulls that excess fluid downward, which is why your legs and feet bear the brunt.
Your lymphatic system acts as a secondary drainage network, collecting excess fluid from tissues and returning it to your bloodstream. When lymph vessels are damaged or overwhelmed, fluid accumulates even faster. This is why swelling tends to worsen throughout the day as you stand or sit upright, and improves overnight when your legs are level with your heart.
One Swollen Leg vs. Both
The single most useful clue is whether one leg is swollen or both. One-sided swelling usually points to a local problem: a blood clot, an injury, an infection, or a blockage in the lymphatic vessels of that leg. Two-sided swelling is more likely a whole-body issue, such as heart, kidney, or liver problems, a medication side effect, or simply prolonged sitting or standing.
This distinction isn’t absolute, but it’s the first thing most clinicians assess and a useful framework for understanding your own symptoms.
Blood Clots: The Red Flag to Rule Out
A deep vein thrombosis (DVT) is a blood clot that forms in the deep veins of your leg. It typically causes sudden swelling in one leg, along with pain or tenderness that may worsen when you stand or walk, warmth over the swollen area, and skin that looks red or discolored. You might also notice veins near the surface appearing larger than usual.
The danger with DVT isn’t just the leg swelling. The clot can break loose and travel to your lungs, causing a pulmonary embolism. Symptoms of that include chest pain, shortness of breath, coughing up blood, lightheadedness, or fainting. If you have sudden one-sided leg swelling combined with any of those symptoms, that warrants emergency care.
DVT is diagnosed with a vascular ultrasound, which shows blood flow and clots in your veins. A blood test called a D-dimer can also help determine whether clotting is occurring. Risk factors include recent surgery, long periods of immobility (like a long flight or bed rest), pregnancy, and certain genetic clotting conditions.
Heart, Kidney, and Liver Problems
When your heart can’t pump blood efficiently, blood backs up in your veins. In congestive heart failure, one or both of the heart’s lower chambers fail to pump well, causing blood to pool in the legs, ankles, and feet. The swelling is usually symmetrical and worsens over the course of the day. You might also feel short of breath, especially when lying flat or during exertion.
Kidney disease causes swelling through a different mechanism. Your kidneys lose the ability to filter excess fluid and salt from your blood, so both accumulate. Kidney-related edema often shows up in the legs and around the eyes. In a more specific form called nephrotic syndrome, damaged kidney filters allow protein to leak into urine, reducing the blood’s ability to pull fluid back from tissues.
Liver damage from cirrhosis can cause fluid to build up in both the abdominal area and the legs. The liver normally produces proteins that help keep fluid inside blood vessels. When it can’t make enough, fluid leaks out more easily.
For people with heart failure, current guidelines recommend keeping sodium intake between 1,500 and 3,000 milligrams per day to help control fluid retention. For context, a single fast-food meal can easily exceed 1,500 mg.
Venous Insufficiency
Chronic venous insufficiency is one of the most common causes of persistent leg swelling, especially in people over 50. The veins in your legs contain one-way valves that push blood upward against gravity. When those valves weaken or fail, blood pools in the lower legs, increasing pressure and forcing fluid into surrounding tissues.
The condition progresses through recognizable stages. Early on, you might notice spider veins or small visible veins near the skin. As it advances, varicose veins (3 mm or larger in diameter) appear, followed by persistent edema. Left untreated, the skin on your lower legs can darken, develop a leathery texture, or even break down into ulcers. The swelling from venous insufficiency tends to build over years, worsen by evening, and improve with leg elevation.
Lymphedema and Lipedema
Lymphedema occurs when the lymphatic drainage system is blocked or damaged, causing protein-rich fluid to accumulate in the tissues. It can result from surgery (particularly lymph node removal during cancer treatment), radiation, infection, or a congenital abnormality. The swelling may start in one leg and often feels firm or spongy rather than soft.
Lipedema is a different condition that’s frequently misdiagnosed as simple weight gain or lymphedema. It involves an abnormal accumulation of fat cells, almost exclusively in the legs (and sometimes arms), and primarily affects women. A few key features help distinguish it from lymphedema:
- Feet are spared. Lipedema creates a distinct “cuff” at the ankles where the swelling stops and the feet appear normal. Lymphedema typically includes the feet.
- The swelling doesn’t pit. Pressing a finger into lipedema-affected tissue won’t leave an indentation, while lymphedema often does.
- The Stemmer sign. In lymphedema, you can’t pinch or tent the skin at the base of the second toe. In lipedema, you can.
Both conditions are chronic and progressive, but they require very different management approaches, so getting the right diagnosis matters.
Medications That Cause Swelling
Several common drug classes can cause leg swelling as a side effect. Blood pressure medications called calcium channel blockers are among the most frequent culprits. These drugs widen arteries but not veins, creating a pressure imbalance that pushes fluid into leg tissues. The effect is not caused by salt and water retention but by this mismatch in vessel dilation. More potent versions of these medications (like amlodipine) cause edema more often than milder ones (like diltiazem).
Other medications linked to leg swelling include NSAIDs (common over-the-counter pain relievers like ibuprofen and naproxen), certain diabetes medications, and some blood pressure drugs like beta blockers and vasodilators. If your leg swelling started around the time you began a new medication, that timing is worth noting and discussing with your prescriber.
How to Check Your Own Swelling
You can perform a simple test at home. Press your thumb firmly into the skin over your shinbone for about five seconds, then release. If the pressure leaves a visible dent that takes time to fill back in, that’s pitting edema. Healthcare providers grade it on a four-point scale:
- Grade 1: A shallow 2 mm dent that rebounds immediately
- Grade 2: A 3 to 4 mm dent that fills in within 15 seconds
- Grade 3: A 5 to 6 mm dent that takes 15 to 60 seconds to rebound
- Grade 4: An 8 mm dent that takes two to three minutes to fill back in
Grade 1 or 2 after a long day on your feet may be nothing to worry about. Grade 3 or 4, or any grade that persists after a night of rest with your legs elevated, suggests something more than simple gravity at work.
Pregnancy-Related Swelling
Some degree of leg swelling is normal during pregnancy, particularly in the third trimester, as the growing uterus compresses veins returning blood from the legs. However, swelling that comes on suddenly, worsens rapidly from your baseline, or appears in your face and hands (not just your legs) can signal preeclampsia, a serious complication involving high blood pressure. Preeclampsia-related swelling is often accompanied by headaches, vision changes, or upper abdominal pain.
Lifestyle Causes and Simple Fixes
Not all leg swelling signals a medical problem. Sitting or standing for extended periods, flying on long flights, eating a high-sodium meal, or being in hot weather can all cause temporary fluid accumulation in your legs. Excess body weight also increases pressure on leg veins.
For mild, gravity-related swelling, a few strategies help. Elevating your legs above heart level for 20 to 30 minutes allows fluid to drain back toward your core. Moving regularly throughout the day activates calf muscles that act as pumps for your veins. Compression stockings apply external pressure that counteracts fluid leaking into tissues. Reducing sodium intake helps your kidneys excrete more fluid rather than holding onto it.
If your swelling is new, persistent, affects only one side, comes with pain or skin changes, or is accompanied by shortness of breath, those patterns point toward causes that need medical evaluation rather than lifestyle adjustments alone.