Swollen ankles and legs happen when excess fluid builds up in the tissues beneath your skin, a condition called edema. The causes range from something as simple as sitting too long to something as serious as heart or kidney disease. Whether the swelling affects one leg or both, came on suddenly or gradually, and whether you have other symptoms all point toward different explanations.
How Fluid Ends Up in Your Legs
Your body constantly moves fluid between your bloodstream and the surrounding tissues. This exchange depends on a balance of pressures inside and outside your blood vessels. When that balance tips, fluid leaks out faster than it can be reabsorbed, and gravity pulls it down to your ankles and legs. The imbalance can come from increased pressure inside blood vessels, weakened vessel walls that let fluid pass through too easily, problems with lymphatic drainage, or low protein levels in the blood that normally help pull fluid back in.
Common Everyday Causes
Most leg swelling isn’t caused by a serious medical condition. Long, unbroken periods of sitting or standing are one of the most frequent triggers. When your legs stay in the same position for hours, your calf muscles aren’t contracting to push blood back up toward your heart, so fluid pools in your lower legs. Desk workers, long-haul travelers, and people who stand all day for work are especially prone to this.
A high-sodium diet is another major contributor. Processed meats, canned soups, chips, cheese, and fast food all pack large amounts of salt that cause your body to hold onto extra water. The American Heart Association recommends no more than 2,300 milligrams of sodium per day, with an ideal target of 1,500 milligrams for most adults. The average American eats well over 3,400 milligrams daily, which is more than enough to cause noticeable fluid retention.
Heat also plays a role. In warm weather, blood vessels near the skin dilate to help cool your body, and some fluid seeps into surrounding tissues. This type of swelling is temporary and usually resolves once you cool down and elevate your legs.
One Leg vs. Both Legs
The pattern of your swelling is one of the most important clues to its cause. Swelling in just one leg raises different concerns than swelling in both.
When a single leg swells suddenly, the most urgent possibility is a deep vein thrombosis (DVT), a blood clot in one of the deep veins of the leg. A DVT typically causes swelling, pain, warmth, and sometimes redness in the affected leg. This needs prompt medical evaluation because the clot can break loose and travel to the lungs. Once a clot is ruled out, the most common explanations for sudden one-sided swelling are muscle strains or tears (about 40% of cases), followed by a category where no clear cause is found (about 26%).
Chronic swelling in one leg most often points to venous insufficiency, where the valves in your leg veins weaken and allow blood to pool instead of flowing back to the heart. Over time, this can cause skin discoloration, thickening, and even ulcers near the ankle. Lymphedema, where the lymphatic drainage system is damaged or blocked, is another possibility, particularly in people who’ve had lymph node removal, radiation therapy, or certain infections.
When both legs swell at the same time, the cause is more likely systemic. Chronic venous disease is still the most common explanation, but heart failure, kidney disease, liver disease, and certain medications all cause bilateral swelling. Heart failure tends to come with shortness of breath, fatigue, and difficulty lying flat. Kidney disease causes the body to retain both salt and fluid. Liver disease can lower blood protein levels, reducing the blood’s ability to hold onto fluid.
Medications That Cause Swelling
Several common prescription drugs list leg swelling as a side effect. Calcium channel blockers, frequently prescribed for high blood pressure, are among the most well-known culprits. These drugs widen certain blood vessels, which increases pressure inside the smallest capillaries and pushes fluid into the surrounding tissue. Diabetes medications in the thiazolidinedione class cause swelling through a different mechanism: they increase the permeability of blood vessel walls and trigger the kidneys to hold onto more sodium and water.
Hormone therapies, including estrogen-containing birth control and hormone replacement, can also contribute. If your swelling started or worsened after beginning a new medication, that connection is worth discussing with your prescriber. Don’t stop a medication on your own, but know that alternatives with fewer fluid-retention effects often exist.
Swelling During Pregnancy
Some degree of ankle and leg swelling is normal during pregnancy, especially in the third trimester. The growing uterus puts pressure on veins that return blood from the legs, and hormonal changes cause the body to retain more fluid overall.
What isn’t normal is sudden swelling, particularly in the face and hands, combined with rapid weight gain. This pattern can signal preeclampsia, a serious pregnancy complication defined by high blood pressure and signs of organ damage, most often protein spilling into the urine. Preeclampsia typically develops after 20 weeks of pregnancy and requires close medical monitoring because it can progress quickly.
How to Check Your Own Swelling
You can do a simple test at home to gauge the severity of your edema. Press a finger firmly into the swollen area for about 10 seconds, then release. If a visible dent remains, you have what’s called pitting edema. The deeper the dent and the longer it takes to spring back, the more fluid is present. A shallow dent that rebounds immediately is mild (grade 1). A deep dent of 8 millimeters or more that takes two to three minutes to refill is severe (grade 4). This test won’t tell you the cause, but it gives you useful language to describe what’s happening when you talk to a healthcare provider.
What You Can Do at Home
For mild, everyday swelling, a few consistent habits make a real difference. Elevating your legs above heart level for about 15 minutes, three to four times a day, helps fluid drain back toward your core. Lie down and prop your legs on a pillow or cushion rather than just resting them on an ottoman at seat height. The key is getting your ankles above the level of your heart.
Movement is equally important. If you sit for long stretches, get up and walk for a few minutes every hour. Even flexing your ankles and calves while seated helps pump blood upward. Cutting back on sodium is one of the most effective dietary changes you can make. Reading nutrition labels and cooking more meals from whole ingredients, rather than relying on packaged or restaurant food, are practical starting points.
Compression stockings provide steady, graduated pressure that supports your veins and prevents fluid from pooling. Over-the-counter options at 15 to 20 mmHg offer mild support and work well for occasional swelling from travel or long days on your feet. For chronic venous insufficiency or more persistent edema, 20 to 30 mmHg is the most commonly prescribed daytime level. Higher pressures (30 to 40 mmHg and above) are reserved for more severe cases and should be fitted with clinical guidance.
Signs That Need Immediate Attention
Most leg swelling develops gradually and isn’t an emergency, but certain combinations of symptoms require urgent care. Seek emergency evaluation if you have sudden, unexplained swelling in just one leg, especially with pain, warmth, or redness, as this could indicate a blood clot. Swelling accompanied by chest pain, trouble breathing, coughing up blood, or fever also warrants an immediate visit. These symptoms can signal a clot that has traveled to the lungs, an infection, or acute heart failure.
Even without those red flags, swelling that persists for more than a few days, keeps getting worse, or leaves your skin looking discolored or thickened is worth having evaluated. Your provider will typically start with a physical exam and may order blood work, an ultrasound of the leg veins, or tests of heart and kidney function depending on the pattern and your other symptoms.
How Persistent Edema Is Treated
When swelling is caused by an underlying condition, treating that condition is the priority. For heart failure or kidney disease, medications called diuretics (often referred to as water pills) help the kidneys flush out excess sodium and water. Different types work on different parts of the kidney, and your provider will choose one based on how well your kidneys are functioning and what other conditions you have.
For chronic venous insufficiency, the mainstay of treatment is compression therapy combined with regular leg elevation and exercise. In more advanced cases, procedures to close or remove damaged veins can improve blood flow and reduce swelling over time. Lymphedema is typically managed with specialized massage techniques, compression garments, and exercise programs designed to encourage lymphatic drainage.
Regardless of the cause, the lifestyle basics of moving regularly, managing sodium intake, and elevating your legs remain part of the treatment plan. These aren’t just stopgaps while you wait for a diagnosis. They’re effective, evidence-based strategies that complement whatever medical treatment you may need.