Feet and ankles swell when fluid leaks out of tiny blood vessels and collects in the surrounding tissue faster than your body can drain it away. This is called edema, and it ranges from a harmless side effect of a long day on your feet to a signal that something more serious is happening with your heart, kidneys, or veins. The cause usually falls into one of a few common categories, and understanding which one applies to you makes a real difference in what to do next.
How Fluid Ends Up Trapped in Your Feet
Your body constantly moves water between your bloodstream and the tissue around it. Two main forces keep this in balance: the pressure of blood pushing fluid out through capillary walls, and proteins in your blood pulling fluid back in. When something tips that balance, fluid escapes into the tissue and stays there. Gravity pulls that excess fluid downward, which is why the feet and ankles are almost always the first place you notice it.
Your lymphatic system acts as a backup drainage network, collecting stray fluid from tissues and returning it to the bloodstream. Edema becomes visible only when the rate of fluid leaking out exceeds what the lymphatic system can handle. That’s why swelling can come from increased pressure pushing fluid out, reduced ability to pull fluid back in, or a sluggish lymphatic system that can’t keep up.
Everyday Causes That Are Usually Harmless
The most common reason for swollen ankles is simply spending too long standing or sitting in one position. When your legs stay still, the calf muscles that normally help pump blood back up toward your heart aren’t doing their job. Blood pools in the lower legs, pressure builds in the veins, and fluid seeps into the surrounding tissue. Long flights, desk jobs, and standing shifts all trigger this.
Heat makes it worse. In warm weather, blood vessels near the skin dilate to release heat, which increases fluid leakage into tissue. Eating a high-sodium meal causes your body to retain extra water, amplifying the effect. And carrying extra body weight puts more pressure on the veins in your legs, making pooling more likely throughout the day.
If your swelling appears in the evening, affects both feet equally, and goes down overnight, these everyday factors are the most likely explanation.
Vein Problems in the Legs
Inside your leg veins, one-way valves open to let blood flow upward toward your heart and close to prevent it from falling back down. When those valves weaken or become damaged, a condition called chronic venous insufficiency (CVI), gravity takes over. Blood flows backward, pools in the lower legs, and raises pressure inside the veins until fluid is forced out through the capillary walls.
CVI tends to develop gradually over years. Early on, you may notice mild ankle swelling that worsens through the day. Over time, the sustained pressure can burst tiny capillaries, causing brownish discoloration on the skin around the ankles. In severe cases, the trapped fluid triggers scar tissue to form in the surrounding tissue, which locks in even more fluid and makes the swelling harder to reverse. Varicose veins, aching legs, and skin that feels tight or itchy are all common alongside the swelling.
Heart, Kidney, and Liver Conditions
When the heart can’t pump blood efficiently, blood backs up in the veins returning to the heart. That backup raises pressure in the leg veins and pushes fluid into the tissue, exactly the same mechanism as vein valve problems but driven from a different source. Heart failure is one of the most important medical causes of bilateral foot and ankle swelling, and it often comes with other signs like shortness of breath, fatigue, or waking up at night needing air.
Kidney disease reduces your body’s ability to filter excess salt and water from the blood. The extra fluid has to go somewhere, and it settles in the lowest points of your body. Liver disease, particularly cirrhosis, cuts production of a key blood protein called albumin that normally pulls fluid back into the bloodstream. When albumin levels drop, fluid leaks out more easily and stays in the tissue. Heart failure itself can also damage the kidneys and liver over time, creating a cycle where fluid retention gets progressively worse.
Medications That Cause Swelling
Several common medications list ankle swelling as a side effect. Blood pressure drugs called calcium channel blockers are among the most frequent culprits. These medications relax blood vessel walls, which lowers blood pressure but also allows more fluid to escape into surrounding tissue. The swelling is dose-related: at low doses, roughly 1 to 15% of people develop ankle edema, but at high long-term doses, that number can climb above 80%. Common names in this class include amlodipine, nifedipine, and felodipine.
Anti-inflammatory painkillers (NSAIDs like ibuprofen and naproxen) cause the kidneys to retain sodium and water, which can produce noticeable swelling. Some diabetes medications, certain antidepressants, and hormonal therapies including estrogen and testosterone can do the same. If your swelling started shortly after beginning or increasing a medication, that connection is worth investigating with whoever prescribed it.
Swelling During Pregnancy
Some degree of foot and ankle swelling is normal during pregnancy, especially in the third trimester. Blood volume increases by nearly 50%, the growing uterus puts pressure on pelvic veins, and hormonal shifts cause blood vessels to relax, all of which promote fluid retention in the lower legs.
What separates normal pregnancy swelling from something concerning is the pattern. Gradual, symmetric swelling in the feet that improves with rest is typical. Sudden swelling, particularly in the face and hands, can be a sign of preeclampsia, a serious blood pressure condition that develops after 20 weeks. Sudden, unexplained weight gain alongside that swelling strengthens the concern. Preeclampsia requires prompt medical evaluation because it can progress quickly.
When Swelling in One Leg Is a Warning Sign
Most benign causes of swelling affect both legs roughly equally. Swelling that appears in only one leg, especially when it comes on quickly, raises the possibility of a deep vein thrombosis (DVT), a blood clot in one of the deep veins of the leg. Along with swelling, DVT often causes pain or cramping that starts in the calf, skin that looks red or purple, and warmth over the affected area. Some clots produce no obvious symptoms at all.
The danger of DVT is that a piece of the clot can break free and travel to the lungs, causing a pulmonary embolism. Warning signs of that complication include sudden shortness of breath, chest pain that worsens when you breathe deeply or cough, a rapid pulse, dizziness or fainting, and coughing up blood. A pulmonary embolism is a medical emergency.
How to Reduce Swelling at Home
Elevating your legs is the simplest and most effective way to drain fluid from swollen feet. The key is getting your feet above the level of your heart, not just propping them on an ottoman. Lying down with your legs on a stack of pillows or a cushion works well. Research shows measurable reductions in leg volume after as little as 20 minutes of elevation, though longer sessions produce better results. Doing this two or three times a day helps prevent fluid from accumulating.
Movement is the other reliable tool. Your calf muscles act as a pump that squeezes blood upward through the veins. Walking, calf raises, or simply flexing your feet while seated all activate that pump. If you sit for long periods at work, getting up and walking for a few minutes every hour makes a noticeable difference over the course of a day.
Compression socks apply steady pressure that helps prevent fluid from leaking into the tissue. They come in different pressure levels measured in millimeters of mercury (mmHg). Low compression (under 20 mmHg) is available over the counter and works well for mild, everyday swelling. Medium compression (20 to 30 mmHg) is better for chronic venous insufficiency or more persistent edema. High compression (above 30 mmHg) is typically reserved for more severe conditions and usually requires a fitting. For the best results, put compression socks on first thing in the morning before swelling has a chance to develop.
Cutting back on sodium helps reduce the total amount of fluid your body retains. Most excess sodium comes from processed and restaurant food rather than the salt shaker, so reading labels and cooking more meals at home tends to have a bigger impact than simply not adding salt at the table. Staying well hydrated sounds counterintuitive, but mild dehydration actually triggers your body to hold onto more water, not less.
Patterns Worth Paying Attention To
Occasional, mild swelling that shows up after a long day and disappears by morning is rarely a sign of disease. The patterns that point to something more serious include swelling that persists even after a night of sleep, swelling that gets progressively worse over weeks, pitting (where pressing a finger into the swollen area leaves a visible dent that takes several seconds to fill back in), and swelling that shows up alongside shortness of breath, chest pain, or reduced urine output.
One-sided swelling with pain or skin color changes warrants urgent attention because of the DVT risk. Swelling that develops rapidly during pregnancy, especially with headaches, vision changes, or upper abdominal pain, needs the same urgency. And if you’re taking a medication known to cause edema, the swelling may be manageable, but it’s still worth bringing up at your next appointment so the benefit of the drug can be weighed against the side effect.