Leg swelling happens when excess fluid builds up in the tissue outside your blood vessels and lymphatic channels. The causes range from spending too long on your feet to serious conditions like heart failure or blood clots. Whether the swelling is in one leg or both, came on suddenly or gradually, and how it responds to elevation all point toward different underlying problems.
How Fluid Ends Up in Your Tissues
Your body constantly moves fluid between your bloodstream and the surrounding tissue. Several forces keep this exchange balanced: the pressure inside your blood vessels pushing fluid out, proteins in your blood pulling fluid back in, the integrity of your vessel walls, and your lymphatic system draining whatever’s left over. Swelling develops when any of these systems tips out of balance.
Increased pressure inside your veins pushes more fluid into the tissue than your body can reabsorb. Low protein levels in your blood (common in liver or kidney disease) reduce the pulling force that draws fluid back into your vessels. Damaged or leaky vessel walls let fluid escape too easily, which happens during infections or allergic reactions. And when your lymphatic system is blocked or damaged, fluid simply has nowhere to drain. Most cases of leg swelling involve one or more of these mechanisms working together.
Heart, Kidney, and Liver Disease
Heart failure is one of the most common systemic causes of leg swelling. When the heart can’t pump effectively, it triggers a chain reaction: the kidneys sense reduced 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 legs. The result is fluid being pushed into the tissue faster than it can be reabsorbed. Heart failure also reduces levels of albumin (a key blood protein), further weakening the body’s ability to keep fluid inside the vessels. Swelling from heart failure is typically in both legs and worsens over the course of the day.
Kidney disease causes swelling through a more direct route. When the kidneys lose their filtering ability, sodium and water accumulate in the body with no way out. In nephrotic syndrome, the kidneys also leak large amounts of protein into the urine, dropping blood protein levels and reducing the force that holds fluid in the bloodstream. This combination of excess fluid and low protein can cause significant swelling in the legs, face, and around the eyes.
Liver cirrhosis creates a similar protein problem. The liver produces albumin, so when it’s severely damaged, albumin levels drop. Cirrhosis also increases pressure in the veins that drain blood from the digestive organs, which redirects fluid into the abdomen (a condition called ascites) and down into the legs.
Vein Problems and Blood Clots
Chronic venous insufficiency develops when the one-way valves inside your leg veins stop working properly. These valves are supposed to keep blood moving upward toward your heart, but when they fail, blood pools in the lower legs. Over time, the sustained pressure damages the smallest blood vessels, pushing fluid into the surrounding tissue. You’ll often notice the swelling gets worse with standing and improves overnight. Skin changes are common too: the skin around the ankles may turn brown or reddish, become thick and leathery, or develop open sores that are slow to heal.
A deep vein thrombosis, or DVT, is a blood clot that forms in one of the deep veins of the leg. It typically causes sudden swelling in just one leg, often with pain, warmth, and redness. This is the most urgent cause of leg swelling to rule out, because the clot can break loose and travel to the lungs. One-sided swelling that comes on quickly, especially after surgery, prolonged immobility, or a long flight, should be evaluated promptly. Doctors use a combination of clinical scoring tools and ultrasound imaging to confirm or rule out a clot.
Lymphedema
Your lymphatic system acts as a secondary drainage network, collecting fluid that your veins don’t reabsorb and returning it to the bloodstream. When lymphatic vessels are damaged or blocked, that fluid accumulates in the tissue. Lymphedema most commonly affects the arms or legs and tends to produce a firmer, heavier type of swelling compared to the soft, pitting swelling seen with vein problems.
In developed countries, the most common cause of lymphedema is cancer treatment, particularly surgery or radiation that removes or damages lymph nodes. It can also develop on its own (primary lymphedema) or as a complication of severe chronic venous insufficiency, a condition called phlebolymphedema, where long-standing vein problems eventually overwhelm the lymphatic system too. Unlike venous swelling, lymphedema doesn’t improve much with elevation alone and generally requires compression therapy and specialized massage techniques to manage.
Medications That Cause Swelling
Several common medications cause fluid retention in the legs as a side effect. Calcium channel blockers, a widely prescribed class of blood pressure drugs, are among the most frequent culprits. Amlodipine, one of the most commonly used options, causes noticeable ankle and foot swelling in nearly half the people who take it. These drugs work by relaxing blood vessel walls, which lowers blood pressure but also increases fluid leakage into the surrounding tissue.
NSAIDs like ibuprofen and naproxen cause the kidneys to retain sodium and water, which can lead to swelling over time, especially with regular use. Hormone therapies (including estrogen-containing birth control and hormone replacement therapy), certain diabetes medications, and some antidepressants can also contribute. If you notice new swelling after starting a medication, it’s worth checking whether it’s a known side effect before pursuing other explanations.
Pregnancy-Related Swelling
Some degree of leg and ankle swelling is normal during pregnancy, particularly in the third trimester. The growing uterus compresses veins in the pelvis, slowing the return of blood from the legs. Blood volume also increases by roughly 50% during pregnancy, adding to the fluid load.
The concern is when swelling signals preeclampsia, a condition involving high blood pressure and, often, protein in the urine. Preeclampsia tends to cause swelling in the hands, arms, and face rather than just the ankles and feet. Rapid swelling, unexplained weight gain over a few days, severe headaches, and vision changes are the key warning signs that distinguish it from routine pregnancy swelling. Ankle swelling by itself, without elevated blood pressure, is almost always benign.
Everyday and Lifestyle Causes
Not all leg swelling points to a medical condition. Gravity is the simplest explanation: standing or sitting for hours without moving allows fluid to pool in your lower legs. This is especially common during long flights, desk jobs, or any situation where the calf muscles aren’t contracting to help push blood back up. Heat also plays a role, since warm temperatures cause blood vessels to dilate and allow more fluid to escape into the tissues. A high-salt diet increases fluid retention throughout the body, and the effects of gravity concentrate that extra fluid in the legs.
Obesity adds mechanical pressure to the veins and lymphatic channels in the pelvis and legs, making it harder for fluid to drain efficiently. This is one of the strongest risk factors for chronic swelling that isn’t explained by a specific disease.
One Leg vs. Both Legs
The pattern of swelling is one of the most useful clues to its cause. Swelling in both legs that develops gradually usually points to a systemic issue: heart failure, kidney disease, liver disease, medication side effects, or venous insufficiency affecting both legs. Sudden worsening of bilateral swelling is often linked to a flare of heart failure or a new medication.
Swelling in just one leg raises different possibilities. A DVT is the first concern with acute, one-sided swelling. Chronic one-sided swelling more often suggests lymphedema, a localized vein problem, or prior damage from an injury or surgery. Infections like cellulitis can also cause rapid, painful swelling in a single leg, usually with redness and warmth.
Reducing Swelling at Home
For mild or lifestyle-related swelling, a few strategies make a real difference. Elevating your legs above heart level for 15 to 30 minutes several times a day helps gravity work in your favor, pulling fluid back toward your core. If lying flat with your legs propped up isn’t practical, resting them on a footstool or ottoman still helps by reducing the amount of pressure pushing fluid downward.
Compression stockings apply graduated pressure to the legs, with the tightest squeeze at the ankle and decreasing pressure moving upward. This supports the veins and prevents fluid from settling in the tissue. They’re particularly effective for chronic venous insufficiency and mild lymphedema. Regular movement matters too: walking, flexing your feet, and contracting your calf muscles all activate the muscle pump that pushes blood back up through your veins. Cutting back on sodium helps reduce overall fluid retention, which can take some of the load off your legs.
Swelling that doesn’t improve with elevation, appears suddenly in one leg, or comes with shortness of breath, chest pain, or skin changes warrants a medical evaluation. Diagnosis typically starts with a physical exam and medical history, and may include blood tests, ultrasound of the leg veins, or other imaging depending on the suspected cause.