Swelling in the legs and feet happens when fluid leaks out of tiny blood vessels and accumulates in the surrounding tissue. The underlying cause can be as simple as sitting too long on a flight or as serious as heart failure or a blood clot. Whether the swelling affects one leg or both, came on suddenly or built up over weeks, and whether it’s paired with other symptoms all point toward different explanations.
How Fluid Ends Up in Your Tissues
Your body constantly moves fluid between your bloodstream and the tissue around it. Three forces keep this exchange in balance: the pressure inside your blood vessels pushing fluid out, proteins in your blood pulling fluid back in, and the walls of your smallest blood vessels acting as a selective barrier. When any of these shifts, fluid seeps into the surrounding tissue faster than your body can clear it.
Your lymphatic system acts as the cleanup crew, collecting excess fluid and filtered proteins from tissues and returning them to the bloodstream. If that drainage system gets blocked or overwhelmed, fluid pools in whatever area gravity pulls it toward, which is usually your feet, ankles, and lower legs.
Vein Problems in the Legs
Chronic venous insufficiency (CVI) is one of the most common causes of persistent leg swelling, affecting roughly 1 in 20 adults. Your leg veins contain one-way valves that push blood upward toward the heart against gravity. When those valves weaken or get damaged, blood flows backward and pools in the lower legs. Over time, the rising pressure inside those veins forces fluid out through capillary walls and into the surrounding tissue.
CVI swelling is typically worst at the end of the day or after long periods of standing. You might also notice skin discoloration around the ankles, a feeling of heaviness in the legs, or visible varicose veins. Left untreated, the sustained pressure can eventually burst the tiniest blood vessels near the skin surface, leading to discoloration and, in advanced cases, open sores.
Blood Clots: One Leg Is a Warning Sign
Deep vein thrombosis (DVT), a blood clot in one of the deep veins of the leg, often causes swelling in just one leg. About 75% of people with DVT have tenderness along the calf muscles or the inner thigh, and about half experience leg pain. The skin over the clot may feel warm or look slightly red. In some cases, swelling is the only noticeable symptom.
The danger with DVT isn’t just the leg. About 10% of people with a confirmed clot develop a pulmonary embolism, where part of the clot breaks loose and travels to the lungs. That’s why sudden, unexplained swelling in a single leg, especially with pain, warmth, or redness, warrants urgent medical evaluation. Clinical signs alone can’t confirm or rule out a clot. Imaging is always needed.
Heart, Kidney, and Liver Disease
When swelling appears in both legs and develops gradually over weeks, an organ-level problem may be driving it.
Heart failure means the heart isn’t pumping blood efficiently. Blood backs up in the veins, raising pressure in the legs, ankles, and feet. The swelling often worsens throughout the day and may be accompanied by shortness of breath, fatigue, or abdominal bloating from fluid buildup around the organs.
Kidney disease impairs the body’s ability to filter excess fluid and salt, which then accumulate in the blood and leak into tissues. Kidney-related swelling tends to show up in the legs and around the eyes. A specific type of kidney damage called nephrotic syndrome causes the kidneys to leak protein into the urine, which lowers the protein levels in the blood that normally pull fluid back into vessels.
Liver disease, particularly cirrhosis, reduces the liver’s ability to produce those same blood proteins. The result is the same: without enough protein in the bloodstream to retain fluid, it escapes into surrounding tissue. Liver-related swelling often includes noticeable abdominal bloating alongside leg edema.
Medications That Cause Swelling
Several common medications list leg or ankle swelling as a side effect. The most well-known culprits are a class of blood pressure drugs called calcium channel blockers. These medications relax blood vessel walls, which can increase fluid leakage at the capillary level. Reported rates of ankle swelling range from 1% to 15% at standard doses, but can exceed 80% in people taking high doses long-term. One clinical trial found that combining the medication with another type of blood pressure drug cut swelling rates from about 19% to under 8%.
Other medications commonly linked to leg swelling include certain diabetes drugs, hormone therapies (including estrogen and testosterone), and over-the-counter pain relievers like ibuprofen and naproxen. Steroids and some antidepressants can also contribute. If you notice new swelling after starting a medication, that timing is worth flagging to your prescriber rather than stopping the drug on your own.
Pregnancy and Preeclampsia
Mild leg and foot swelling during pregnancy is extremely common, especially in the third trimester. The growing uterus puts pressure on the veins that return blood from the legs, and hormonal changes cause the body to retain more fluid overall. This type of swelling is usually harmless.
The concern arises when swelling appears suddenly in the face or hands during the second half of pregnancy, which can signal preeclampsia, a condition involving dangerously high blood pressure. Preeclampsia can harm both the mother and baby if not caught early. Rapid or unusual swelling paired with headaches, vision changes, or upper abdominal pain during pregnancy is a reason to contact your provider immediately.
Everyday Triggers
Not all leg swelling points to a medical condition. Gravity alone can do it. Sitting for hours on a long flight, standing all day at work, or spending an evening on the couch without moving your legs allows fluid to pool in your lower extremities. Obesity adds constant pressure to the veins in the legs and pelvis, making it harder for blood to travel back to the heart efficiently. A high-sodium diet compounds the problem by causing your body to retain extra fluid.
Hot weather is another common trigger. Heat causes blood vessels to dilate, which lowers the pressure that keeps fluid inside them. Many people notice their shoes feel tighter on summer evenings than they do in cooler months.
One Leg vs. Both Legs
The pattern of swelling is one of the most useful clues to its cause. Swelling in just one leg typically points to a local problem: a blood clot, an injury, an infection, or a blockage in the lymphatic drainage on that side. Swelling in both legs is more likely tied to a systemic issue like heart failure, kidney disease, venous insufficiency, medication side effects, or prolonged inactivity.
There are exceptions. Venous insufficiency can sometimes affect one leg more than the other, and lymphedema can be one-sided or bilateral depending on the cause. But as a general rule, symmetry matters and is one of the first things a clinician will assess.
Managing Swelling at Home
For mild, non-urgent swelling, a few strategies can make a noticeable difference. Elevating your legs above heart level for about 15 minutes, three to four times a day, helps gravity drain fluid back toward the core. Lie flat and prop your legs on a pillow or cushion so your ankles sit higher than your chest.
Reducing sodium intake is another effective lever. For people prone to fluid retention, guidelines from the Heart Failure Society of America recommend keeping sodium between 2,000 and 3,000 milligrams per day, with a stricter limit of under 2,000 milligrams for moderate to severe heart failure. Most of the sodium in a typical diet comes from processed and restaurant foods rather than the salt shaker.
Compression stockings apply graduated pressure to the legs, pushing fluid upward and preventing it from pooling. Mild compression (8 to 15 mmHg) works well for tired legs, minor swelling, or long travel days. Firmer compression (30 to 40 mmHg) is used for severe edema and chronic venous insufficiency, but requires guidance from a healthcare provider to ensure proper fit and avoid complications. Regular movement, even short walks or calf raises throughout the day, activates the muscle pump in your lower legs that helps push blood back toward the heart.