Leg swelling below the knee happens when fluid accumulates in the tissues of your lower leg, ankles, or feet. The most common causes range from simply standing too long to chronic conditions like venous insufficiency, heart failure, and kidney or liver disease. Whether the swelling affects one leg or both is one of the most important clues to its cause.
How Fluid Builds Up in Your Lower Legs
Your lower legs are the lowest point in your body when you’re upright, which makes them especially vulnerable to fluid accumulation. Normally, a balance of pressures inside your blood vessels keeps fluid where it belongs. Blood pressure pushes fluid outward through capillary walls, while proteins in your blood (primarily albumin) pull fluid back in. When either side of that equation shifts, fluid leaks into the surrounding tissue and pools in your lower legs.
Three main mechanisms drive this process. First, increased pressure inside the veins of your legs forces more fluid out than your body can reabsorb. Second, a drop in blood protein levels weakens the pull that keeps fluid inside your vessels. Third, damage to your lymphatic system, which normally drains excess fluid from tissues, allows it to accumulate instead. Most causes of below-the-knee swelling trace back to one or more of these mechanisms.
Chronic Venous Insufficiency
Chronic venous insufficiency (CVI) is one of the most common causes of persistent lower leg swelling. An estimated 10% to 35% of U.S. adults have it, and the prevalence climbs with age. In adults 65 and older, about 4% develop venous ulcers as a complication.
Your leg veins contain one-way valves that push blood upward toward your heart against gravity. When those valves weaken or the veins stretch too wide for the valve flaps to meet, blood flows backward and pools in the lower leg. This creates sustained high pressure in the veins, which forces fluid into the surrounding tissue. The swelling typically worsens throughout the day, especially if you’ve been on your feet, and improves overnight when your legs are elevated.
Over time, CVI can cause visible changes beyond swelling: darkened or reddish-brown skin around the ankles, a heavy or aching sensation in the legs, and in advanced cases, open sores near the ankle that are slow to heal. The condition tends to affect both legs, though one side can be worse than the other.
Blood Clots in the Leg
Deep vein thrombosis (DVT) is a blood clot that forms in a deep vein, most often in the calf or thigh. Unlike the gradual, bilateral swelling of venous insufficiency, DVT typically causes sudden swelling in one leg. The affected leg may feel warm to the touch, and you might notice pain or soreness that starts in the calf and feels like a deep cramp.
DVT is a medical emergency because the clot can break loose and travel to the lungs, causing a pulmonary embolism. If you have sudden one-sided leg swelling along with chest pain, difficulty breathing, dizziness, or coughing up blood, call 911. Risk factors for DVT include recent surgery, long periods of immobility (such as a long flight), cancer, pregnancy, and use of hormonal birth control.
Heart Failure
When the heart can’t pump blood effectively, the reduced output triggers a chain reaction throughout the body. Your kidneys detect the drop in blood flow and respond by holding onto sodium and water, expanding your total fluid volume. At the same time, blood backs up in the veins, raising pressure in the vessels of your lower legs. The combination of extra fluid and higher venous pressure pushes fluid into the tissues of your feet, ankles, and calves.
Swelling from heart failure is usually symmetrical, affecting both legs equally. It often leaves a temporary dent when you press a finger into the skin (called pitting edema). You might also notice that the swelling is worse at the end of the day and that your shoes feel tighter in the evening. Other signs that point toward heart failure include shortness of breath during activity or when lying flat, persistent fatigue, and waking up at night gasping for air.
Kidney and Liver Disease
Both kidney disease and liver disease cause swelling through the same core mechanism: a drop in albumin, the protein responsible for about 80% of the pulling force that keeps fluid inside your blood vessels.
In nephrotic syndrome, a kidney condition, large amounts of protein leak into the urine. The resulting drop in blood albumin weakens the osmotic pull, and fluid shifts into the tissues. Swelling often appears in the legs and around the eyes, sometimes accompanied by foamy urine.
Advanced liver cirrhosis also leads to low albumin because the damaged liver can no longer produce enough of it. People with cirrhosis often develop swelling in both the abdomen and the lower legs. In either case, the edema tends to be widespread rather than limited to one leg.
Lymphedema
Your lymphatic system acts as a drainage network, collecting excess fluid from tissues and returning it to the bloodstream. When lymph vessels or nodes are damaged or blocked, fluid backs up in the affected area. This is lymphedema, and it most commonly affects the legs.
Lymphedema can result from cancer treatment that involves removing lymph nodes, radiation therapy, infections, or in some cases, it develops without a clear trigger. The swelling tends to feel firmer than fluid retention from venous or heart problems. Over time, the skin may thicken and harden, a change known as fibrosis. In severe cases, the skin takes on a rough, thickened texture. Unlike venous edema, lymphedema doesn’t always improve fully with elevation alone.
Medications That Cause Lower Leg Swelling
Several common medications list leg swelling as a side effect. Calcium channel blockers, a class of blood pressure medications that includes amlodipine, are among the most frequent culprits. About 12% of people taking these drugs develop lower leg edema, and the risk increases with higher doses and longer use. The swelling occurs because these medications relax blood vessel walls, which increases the pressure gradient that pushes fluid into surrounding tissue.
Other medications that can cause leg swelling include certain diabetes drugs, nonsteroidal anti-inflammatory drugs (NSAIDs like ibuprofen), steroids, and some hormone therapies. If you notice new leg swelling after starting a medication, it’s worth discussing with your prescriber. Stopping or switching the medication often resolves the problem.
Prolonged Sitting and Standing
Even in healthy people, staying in one position for hours causes measurable swelling in the lower legs. Gravity continuously pulls blood and fluid downward, and without the muscle contractions of walking or moving, your veins lose the pumping assistance they rely on to push blood back up. The result is a slow increase in lower leg volume over the course of a workday.
This type of swelling is temporary and resolves with movement or elevation. It’s more pronounced in warm weather, during pregnancy, and in people who carry extra body weight. If your job involves long hours of sitting or standing, breaking up your position regularly is one of the most effective preventive measures.
Managing Lower Leg Swelling
The right approach depends entirely on the cause, but a few strategies help across most types of lower leg edema. Elevating your legs above heart level for 20 to 30 minutes several times a day reduces the hydrostatic pressure that drives fluid into tissues. Regular movement, even short walks or calf raises, activates the muscle pump that helps push blood and fluid upward.
Compression stockings are one of the most studied and effective tools for managing and preventing lower leg swelling. Stockings in the 15 to 20 mmHg range significantly reduce swelling in people who sit or stand for long periods, and 20 to 30 mmHg stockings provide even greater benefit. Research suggests that pressures as low as 10 to 15 mmHg can be effective for preventing mild occupational swelling, while higher pressures tend to work better for people who spend most of their day seated. Knee-length stockings are sufficient for below-the-knee swelling.
For swelling caused by an underlying condition like heart failure, kidney disease, or venous insufficiency, treating the root cause is essential. Compression and elevation help manage symptoms, but they don’t replace addressing the condition driving the fluid retention.
One Leg vs. Both Legs
The pattern of swelling is one of the most useful diagnostic clues. Swelling in just one leg raises concern for DVT, a localized infection, a calf injury, or lymphedema affecting that limb. It warrants prompt medical evaluation, especially if it appeared suddenly or comes with pain, warmth, or redness.
Swelling in both legs points more toward systemic causes: venous insufficiency, heart failure, kidney or liver disease, medication side effects, or the gravitational effects of prolonged sitting or standing. Bilateral swelling that develops gradually and worsens over weeks or months suggests a chronic condition rather than an emergency, but it still deserves investigation to identify and treat the underlying cause.