A swollen lower leg usually means fluid is building up in the tissue between your skin and muscle, a condition called edema. The cause can be as simple as sitting too long on a flight or as serious as a blood clot. Whether one leg is swollen or both, and whether the swelling came on suddenly or gradually, tells you a lot about what’s going on.
One Leg vs. Both Legs: Why It Matters
The single most useful clue is whether the swelling affects one leg or both. One-sided swelling usually points to a local problem: a blood clot, an injury, an infection, or a blockage in the lymph system on that side. Swelling in both legs at once is more likely driven by something systemic, like heart trouble, kidney issues, or a medication side effect. This distinction won’t give you a diagnosis on its own, but it narrows the possibilities quickly.
Blood Clots in the Deep Veins
A deep vein thrombosis (DVT) is a blood clot that forms in one of the large veins of the leg, most often in the calf or thigh. It typically causes swelling in just one leg along with pain or cramping that starts in the calf, warmth over the affected area, and a color change in the skin (red or purplish, depending on your skin tone). DVT is more common after long periods of immobility, surgery, pregnancy, or in people who smoke or take certain hormonal medications.
The danger with DVT isn’t the clot itself but the possibility that a piece breaks off and travels to the lungs. This is a pulmonary embolism, and it comes on suddenly: sharp chest pain that worsens when you breathe in, unexpected shortness of breath even at rest, a racing heartbeat, coughing (sometimes with blood), and pale or bluish skin. These symptoms need emergency care immediately.
Weak Vein Valves and Chronic Swelling
Your leg veins contain one-way valves that push blood upward toward your heart against gravity. When those valves weaken or get damaged, blood flows backward and pools in the lower leg. This is chronic venous insufficiency, one of the most common reasons for persistent lower leg swelling that gets worse as the day goes on and improves overnight.
Over time, the backward flow of blood raises the pressure inside your leg veins so much that the tiniest blood vessels, capillaries, start to leak or even burst. You might notice aching or heaviness in your legs, visible varicose veins, skin that looks darker or more discolored around the ankles, and in advanced cases, open sores near the ankle that are slow to heal. The swelling is usually in both legs, though it can be worse on one side.
Heart Failure
When the heart can’t pump blood efficiently, fluid backs up into the lungs, legs, and feet. Swelling from heart failure is almost always in both legs and tends to worsen throughout the day or after standing. It’s often accompanied by shortness of breath (especially when lying flat or at night), fatigue, chest pain, or heart palpitations. The leg swelling alone isn’t enough to suspect heart failure, but paired with breathing problems, it’s a combination worth taking seriously.
Medication Side Effects
Certain blood pressure medications, particularly a class called calcium channel blockers, are well-known culprits. These drugs relax blood vessels, which can cause fluid to leak into the surrounding tissue. The swelling typically shows up around the ankles and is usually painless.
At standard doses, somewhere between 1% and 15% of people taking these medications develop ankle swelling. At higher doses over longer periods, that number can climb above 80%. Adding a second type of blood pressure medication (an ACE inhibitor or ARB) can cut the swelling risk by about 38%. If you started a new medication in the weeks before the swelling appeared, that connection is worth exploring with whoever prescribed it. Other drugs that can cause leg swelling include steroids, some diabetes medications, and nonsteroidal anti-inflammatory drugs like ibuprofen.
Lymphedema
Your lymphatic system drains excess fluid from your tissues. When it’s damaged or blocked, fluid accumulates and the affected area swells. Lymphedema in the lower leg often starts with a feeling of heaviness and mild puffiness that gradually worsens. Unlike regular swelling, lymphedema tends to involve the foot and toes in a characteristic way: the top of the foot looks squared off, and the toes appear boxy or swollen.
One way to distinguish lymphedema from other types of swelling is by gently pinching the skin over the top of the second toe. In lymphedema, the skin is too thick and firm to pinch up (this is called the Stemmer sign). Early on, the swelling may be soft and leave a dent when you press it, but over time the skin becomes thick, tough, and fibrotic. Lymphedema can result from surgery (especially cancer surgery involving lymph nodes), radiation, infection, or sometimes has no identifiable cause.
Low Blood Protein
Albumin, a protein made by the liver, acts like a sponge that holds fluid inside your blood vessels. When albumin levels drop, whether from liver disease, kidney disease, or severe malnutrition, fluid escapes into surrounding tissues. The result is usually soft, painless swelling in both legs. Low albumin alone isn’t always enough to cause visible swelling; other factors like inflammation or changes in the tissue itself play a role too. But when paired with a puffy face, swollen hands, or a distended belly, it suggests the body isn’t holding onto protein the way it should.
Pitting vs. Non-Pitting Swelling
When you press a finger into a swollen area and hold it for several seconds, what happens next is diagnostically useful. If the skin holds an indentation (a “pit”) after you release, that’s pitting edema, which is the most common type and occurs with venous insufficiency, heart failure, and many other causes. Clinicians grade it on a scale from 1+ (barely visible, slight pitting) to 4+ (severe swelling that extends above the knee with deep pitting).
If the skin bounces back immediately and won’t hold a dent, that’s non-pitting edema. This pattern is more typical of lymphedema (especially later stages) or thyroid-related swelling. Knowing which type you have helps point toward the right cause.
What Helps Reduce the Swelling
Elevating your legs above heart level for about 15 minutes, three to four times a day, is one of the simplest and most effective ways to reduce fluid buildup. Lying on a couch with your feet propped on pillows works, or lying on the floor with your legs resting up against a wall. The key is getting your legs higher than your chest so gravity can help drain the fluid back toward your heart.
Compression stockings apply steady pressure to your legs and help prevent fluid from pooling. They come in several pressure levels. Mild support (15 to 20 mmHg) is the lightest grade and is often used for travel, minor swelling, or tired legs. Moderate compression (20 to 30 mmHg) is the most commonly prescribed level for everyday management of lower leg swelling. Firmer grades (30 to 40 mmHg and above) are reserved for more severe swelling, significant venous insufficiency, or lymphedema, and should be fitted based on clinical assessment.
Reducing salt intake helps because sodium causes your body to retain water. Staying active, even with short walks or calf exercises, keeps the muscle pump in your legs working, which pushes fluid back up through your veins. Avoiding long stretches of sitting or standing without movement makes a noticeable difference for most people.
Signs That Need Prompt Attention
Swelling in one leg that appears suddenly, especially with calf pain, warmth, or skin color changes, raises concern for a blood clot. Swelling in both legs paired with shortness of breath, difficulty breathing at night, or chest pain could signal heart failure. Any leg swelling accompanied by fever, redness spreading outward, or skin that feels hot may indicate an infection. And if you develop sudden chest pain, rapid breathing, or cough up blood while dealing with a swollen leg, that combination suggests a clot may have reached the lungs and requires emergency care.