Swelling in the lower legs, from the knee down to the ankles and feet, happens when fluid builds up in the tissue. The causes range from something as simple as sitting too long to serious conditions like blood clots or heart failure. Whether one leg is swollen or both, and whether the swelling came on suddenly or gradually, tells you a lot about what’s behind it.
Why One Leg vs. Both Legs Matters
One of the most useful clues is whether the swelling affects one leg or both. Sudden swelling in a single leg often points to a localized problem: a blood clot, an injury, an infection, or a blockage in the lymphatic system on that side. Chronic swelling in both legs typically signals a systemic issue, something affecting your whole body like heart failure, kidney disease, or problems with your veins.
This distinction is the first thing a doctor evaluates. If swelling has lasted longer than three months, it’s generally classified as chronic edema, and the diagnostic workup shifts toward long-term conditions rather than acute emergencies.
Venous Insufficiency
The most common reason for persistent lower leg swelling is chronic venous insufficiency, which affects roughly 1 in 20 adults. Your leg veins contain one-way valves that push blood upward toward your heart against gravity. When those valves become damaged, they can’t close properly. Blood flows backward and pools in the lower legs, forcing fluid out of the veins and into the surrounding tissue.
You’ll typically notice swelling that worsens throughout the day, especially if you’ve been standing or sitting for long periods. The skin on your lower legs may darken over time, feel itchy, or develop a leathery texture. Varicose veins often accompany venous insufficiency, though they don’t always. The swelling usually improves overnight when your legs are elevated and level with your heart.
Blood Clots (DVT)
A deep vein thrombosis, or DVT, is a blood clot that forms in one of the deep veins of your leg. It’s one of the more dangerous causes of lower leg swelling because the clot can break loose and travel to your lungs. DVT usually affects one leg and comes on relatively quickly.
The hallmark signs include leg pain or cramping that often starts in the calf, swelling, warmth in the affected leg, and a change in skin color (reddish or purplish). Risk factors include recent surgery, prolonged immobility like a long flight or hospital stay, and injury to the veins. If you notice sudden swelling in one leg along with pain and warmth, that warrants urgent medical attention.
If leg swelling is ever accompanied by chest pain, difficulty breathing, coughing up blood, or fainting, call emergency services. These can be signs that a clot has reached the lungs.
Heart Failure
When the heart can’t pump blood efficiently, pressure builds in the veins. That increased pressure pushes fluid out of blood vessels and into the tissues of your lower legs and ankles. The body also responds to reduced blood flow by retaining sodium and water through a cascade of hormonal signals, which makes the swelling worse.
Heart failure typically causes swelling in both legs. It’s often accompanied by shortness of breath (particularly when lying flat or during physical activity), fatigue, and sometimes a persistent cough. The swelling tends to be “pitting,” meaning if you press a finger into the swollen area, it leaves an indentation that takes a few seconds to fill back in. If you’re experiencing leg swelling alongside breathlessness or unusual fatigue, those symptoms together are worth taking seriously.
Kidney and Liver Disease
Your kidneys regulate how much fluid and salt stay in your blood. When kidney function declines, fluid and salts build up, and the excess gets pushed into your tissues. Kidney-related swelling commonly appears in the legs and around the eyes.
A specific form of kidney damage called nephrotic syndrome causes your kidneys to leak protein into your urine. Low protein levels in your blood reduce the force that normally keeps fluid inside your blood vessels, so fluid seeps out into surrounding tissue. Severe, long-term protein deficiency from other causes can produce the same effect.
Liver disease works through a similar mechanism. A damaged liver produces less albumin (the main protein that holds fluid in your bloodstream), leading to fluid accumulation in the legs and abdomen.
Lymphedema
Your lymphatic system acts as a drainage network, collecting excess fluid from tissues and returning it to your bloodstream. When this system is damaged or blocked, fluid accumulates in the affected area. In the lower legs, lymphedema produces a distinctive type of swelling that feels firm rather than squishy and doesn’t leave a dent when you press it (non-pitting edema).
Over time, the skin in the affected area can thicken, harden, and develop a rough texture. In severe cases, the skin resembles the hide of an elephant. Lymphedema can be inherited or can develop after surgery, radiation treatment for cancer, infection, or trauma that damages lymph nodes or vessels. It often starts in one leg and can worsen progressively if not managed with compression therapy and specialized massage techniques.
Medications That Cause Lower Leg Swelling
Several common medications list leg and ankle swelling as a side effect. The most notorious are calcium channel blockers used for blood pressure, particularly amlodipine. Nearly half of people taking this class of drug experience some degree of foot and ankle swelling.
Other medications that can cause lower leg swelling include:
- Other blood pressure drugs: beta blockers, clonidine, hydralazine, minoxidil
- Hormone-based medications: corticosteroids, estrogen, progesterone, testosterone
- Nerve pain and seizure drugs: gabapentin and pregabalin
- NSAIDs: ibuprofen, naproxen, and similar anti-inflammatory painkillers
- Certain antidepressants and Parkinson’s drugs: MAOIs and pramipexole
If your swelling started shortly after beginning a new medication, that connection is worth discussing with whoever prescribed it. Stopping or switching the drug often resolves the swelling, but don’t adjust your medications on your own.
Prolonged Sitting and Standing
Even without an underlying condition, gravity alone can cause fluid to pool in your lower legs. Sitting at a desk for hours, taking a long flight, or standing in one position all day forces your circulatory system to work harder to push blood and fluid back up from your feet. Your calf muscles normally act as a pump for your veins, contracting with each step to squeeze blood upward. When you’re not moving, that pump doesn’t engage.
This type of swelling is usually mild, affects both legs equally, and resolves once you move around or elevate your legs. It becomes more common with age, during pregnancy, and in people carrying extra weight. Frequent breaks to walk, ankle circles while seated, and elevating your legs at the end of the day all help.
How Pitting Edema Is Graded
When you visit a doctor for leg swelling, one of the first things they’ll do is press a finger into the swollen area for several seconds and observe what happens. This test distinguishes pitting edema (the skin holds an indentation) from non-pitting edema (common in lymphedema and thyroid conditions). Pitting edema is graded on a 1 to 4 scale:
- Grade 1: A shallow 2 mm dent that rebounds immediately
- Grade 2: A 3 to 4 mm dent that fills back in within 15 seconds
- Grade 3: A 5 to 6 mm dent that takes up to 60 seconds to rebound
- Grade 4: An 8 mm dent that persists for two to three minutes
Higher grades generally indicate more significant fluid retention and point toward systemic causes like heart, kidney, or liver disease. The evaluation also includes checking whether the swelling is symmetrical, examining for skin changes, and reviewing your medications, surgical history, and any recent periods of immobility.