Leg edema happens when fluid leaks out of your blood vessels and gets trapped in the surrounding tissue. The cause can be as simple as sitting too long or as serious as heart failure, so the pattern of your swelling, whether it affects one leg or both, and any other symptoms you’re experiencing all matter when narrowing down what’s going on.
How Fluid Ends Up in Your Legs
Your body constantly moves fluid between your bloodstream and your tissues. Two forces keep this process balanced: pressure inside your blood vessels pushes fluid out, while proteins (mainly albumin) in your blood pull fluid back in. When either side of that equation shifts, fluid accumulates in tissues instead of staying in circulation.
Several things can tip that balance. Anything that raises pressure inside your veins, like blood backing up from a weak heart or a blocked vein, forces more fluid out into surrounding tissue. On the other side, if your blood protein levels drop too low (below about 2 grams per deciliter), there isn’t enough pull to draw fluid back into your vessels. Gravity does the rest: fluid naturally pools in the lowest point of your body, which is your legs and feet when you’re upright.
Venous Insufficiency: The Most Common Culprit
Chronic venous insufficiency is the single most frequent cause of leg edema. Your leg veins contain one-way valves that push blood upward toward your heart and prevent it from falling back down. When those valves weaken or widen, blood flows backward and pools in your lower legs. This raises pressure inside the veins and pushes fluid into surrounding tissue.
Valve damage often traces back to a prior blood clot (deep vein thrombosis), which scars the vein walls and prevents the valves from closing properly. But it can also happen gradually from aging, obesity, or prolonged standing. Your calf muscles act as a pump that squeezes blood upward with each step, so people who are sedentary or who stand in one position for hours lose that pumping action, and swelling gets worse throughout the day.
You’ll typically notice swelling that improves overnight and returns by evening. Over time, the skin on your lower legs may darken or feel thick and leathery, and you might develop varicose veins.
Heart, Kidney, and Liver Problems
When the heart can’t pump blood efficiently, pressure builds in the veins leading back to it. That elevated pressure transmits all the way down to the legs. Heart failure also triggers a chain reaction: your kidneys sense reduced blood flow and respond by holding onto sodium and water, which expands your blood volume and makes the swelling worse. Normally your body produces hormones that signal the kidneys to release extra sodium, but in heart failure, the kidneys become resistant to those signals, even when hormone levels are extremely high.
Kidney disease causes edema through a different route. Damaged kidneys either can’t filter sodium properly or leak large amounts of protein into the urine. Losing protein drops the pulling force inside your blood vessels, and fluid escapes into tissue. Liver disease, particularly cirrhosis, creates a similar problem because the liver is where albumin is made. When liver function declines, albumin production falls, and fluid shifts out of the bloodstream. Cirrhosis also raises pressure in the veins draining the abdomen, which backs up into the legs.
Edema from these organ problems is almost always bilateral, meaning both legs swell roughly equally. If your swelling came on gradually over weeks and affects both sides, a systemic cause like one of these is more likely than a local vein problem.
Medications That Cause Swelling
Several common medications cause leg edema as a side effect. The most notorious are calcium channel blockers used for high blood pressure, particularly amlodipine, nifedipine, and felodipine. These drugs relax the arteries but not the veins, which creates a pressure imbalance that pushes fluid into tissue. An important detail: this type of edema isn’t caused by excess fluid in your bloodstream, so water pills (diuretics) generally don’t help.
Other medications that commonly cause dose-related leg swelling include:
- NSAIDs like ibuprofen and naproxen
- Steroid hormones including corticosteroids and estrogen-based medications
- Diabetes drugs in the thiazolidinedione class
- Blood pressure medications such as hydralazine and minoxidil
If your leg swelling started within weeks of beginning a new medication or increasing a dose, that timing is worth flagging with your prescriber.
One Leg vs. Both Legs
Whether one or both legs are swollen is one of the most useful clues for figuring out the cause. Swelling in both legs usually points to a systemic issue: heart failure, kidney disease, liver disease, medication side effects, or prolonged sitting. Swelling in just one leg raises concern for a localized problem, and the most urgent of those is a deep vein thrombosis (DVT), a blood clot in a deep leg vein.
DVT symptoms include swelling in one leg, pain or cramping that often starts in the calf, skin that feels warm to the touch, and a color change to red or purple. Some DVTs cause no noticeable symptoms at all, which is part of what makes them dangerous. The risk is that a clot can break free and travel to the lungs. If you have sudden, unexplained swelling in one leg, especially with pain or warmth, that warrants same-day medical evaluation.
Other causes of one-sided swelling include a localized infection (cellulitis), a Baker’s cyst behind the knee, or chronic venous insufficiency that’s worse on one side due to prior vein damage.
What Pitting Edema Tells You
If you press your finger into your swollen shin for a few seconds and it leaves a visible dent, that’s called pitting edema. Healthcare providers grade it on a four-point scale based on how deep the pit is and how long it takes to bounce back:
- Grade 1: A shallow 2 mm pit that rebounds immediately
- Grade 2: A 3 to 4 mm pit that fills back in under 15 seconds
- Grade 3: A 5 to 6 mm pit that takes 15 to 60 seconds to rebound
- Grade 4: An 8 mm pit that takes two to three minutes to fill
Higher grades indicate more fluid in the tissue and often suggest a more significant underlying cause. If you can press a deep dent into your leg that lasts a full minute or longer, that’s worth bringing up sooner rather than later.
Reducing Swelling at Home
The right approach depends on the cause, but several strategies help across most types of leg edema.
Reducing sodium intake is one of the most effective changes you can make. For people with edema, a daily sodium target of roughly 1,400 to 1,800 mg is generally recommended. That’s significantly less than the average intake, which hovers around 3,400 mg for most adults. Processed foods, restaurant meals, and canned soups are the biggest sources, so cooking at home with fresh ingredients makes the biggest dent.
Compression stockings apply external pressure to your legs that counteracts the fluid leaking out of your veins. Light compression in the 10 to 15 mmHg range is effective for preventing swelling from prolonged sitting or standing. Stockings in the 15 to 20 mmHg range provide a noticeable reduction in existing swelling, and 20 to 30 mmHg stockings work better for people who sit most of the day or have moderate venous insufficiency. Knee-high stockings are sufficient for most people. Put them on first thing in the morning before swelling starts, since they’re much harder to pull on over an already swollen leg.
Elevating your legs above heart level for 20 to 30 minutes several times a day lets gravity work in your favor. Resistance exercises that strengthen your calf muscles improve the pumping action that moves blood back up toward your heart, which is especially helpful for venous insufficiency. Even simple calf raises or regular walking can make a measurable difference over time.
Signs That Need Urgent Attention
Leg swelling combined with shortness of breath is a red flag. When excess fluid backs up not just into the legs but also into the lungs, it causes a condition called pulmonary edema. Warning signs include difficulty breathing when lying flat, waking up one to two hours after falling asleep gasping for air, gurgling or wheezing sounds when you breathe, or being unable to speak in full sentences because you can’t catch your breath. Coughing up blood or pink, frothy mucus is another serious sign. These symptoms indicate that your heart or lungs are in acute distress and require emergency care.
Sudden swelling in one leg with pain, warmth, or skin discoloration also warrants prompt evaluation to rule out a blood clot. And any new leg swelling that develops rapidly over days, rather than gradually over weeks, deserves medical attention regardless of whether it affects one leg or both.