Foot swelling happens when excess fluid builds up in the tissues of your feet and ankles. The underlying cause can be as simple as standing too long or as serious as a blood clot or heart failure. Whether one foot or both are swollen, and how quickly the swelling appeared, are the two most important clues to figuring out what’s going on.
How Fluid Ends Up in Your Feet
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. Swelling occurs when that balance tips in one of several ways: pressure inside the veins gets too high, the walls of blood vessels become too leaky, proteins that normally hold fluid in the bloodstream drop too low, or the lymphatic system (your body’s drainage network) can’t keep up.
Gravity plays a major role. Because your feet are the lowest point of your body, they’re where fluid naturally collects when any of these mechanisms goes wrong. That’s why swelling tends to worsen throughout the day and improve overnight while you’re lying flat.
One Foot vs. Both Feet
This distinction matters more than most people realize. Swelling in both feet usually points to a body-wide issue: a heart, kidney, or liver problem, a medication side effect, or prolonged sitting or standing. Swelling in just one foot is more likely caused by something local, like an injury, infection, or blood clot. Knowing which pattern you have helps narrow the list of possibilities considerably.
Heart, Kidney, and Liver Problems
Heart failure is one of the most common medical causes of foot swelling. When the heart can’t pump blood efficiently, flow slows down and blood backs up in the veins returning from your legs. Fluid then leaks out of those veins and collects in the surrounding tissue. You might also notice shortness of breath, fatigue, or swelling that gets worse when you lie flat.
Kidney disease causes swelling differently. When the kidneys can’t filter properly, they retain sodium and water, increasing your overall fluid volume. The extra fluid has to go somewhere, and gravity pulls it to your feet and ankles. Liver disease, particularly cirrhosis, reduces production of a key blood protein called albumin. Albumin acts like a sponge that keeps fluid inside your blood vessels. When levels drop, fluid seeps into tissues throughout the body, often showing up first in the feet and abdomen.
Vein Problems in the Legs
Your leg veins have one-way valves that push blood upward toward your heart, fighting gravity with every heartbeat. Chronic venous insufficiency develops when those valves become damaged and can’t close properly. Blood flows backward and pools in the lower legs, a process called venous reflux. The resulting high pressure in the veins forces fluid out into the surrounding tissue, causing persistent swelling that typically worsens as the day goes on.
Over time, venous insufficiency can also cause skin changes around your ankles: darkening, thickening, or even open sores. Varicose veins are a visible sign that your valves aren’t working well, though you can have valve problems without visible varicose veins. Risk factors include a history of blood clots, obesity, pregnancy, and jobs that require long hours of standing.
Blood Clots: The Red Flag
A deep vein thrombosis (DVT) is a blood clot that forms in a deep leg vein, and it’s the most urgent cause of sudden swelling in one foot or leg. Along with swelling, DVT typically causes pain or cramping (often starting in the calf), warmth in the affected area, and skin that looks red or purple.
The danger isn’t just the clot itself. If a piece breaks off and travels to the lungs, it becomes a pulmonary embolism, which can be life-threatening. Warning signs of that complication include sudden shortness of breath, chest pain that worsens with deep breaths or coughing, a rapid pulse, dizziness, or coughing up blood. Any combination of leg swelling with these symptoms is a medical emergency.
Lymphedema
When the lymphatic system can’t drain fluid properly, a specific type of swelling called lymphedema develops. Unlike swelling from vein problems (which is soft and leaves an indent when you press on it), lymphedema eventually makes the skin feel thick and firm. In advanced stages, you can’t pinch the skin at the base of the second toe between your fingers because the tissue underneath has become fibrotic and stiff.
Lymphedema can develop after surgery that removes lymph nodes (common after cancer treatment), after radiation therapy, or from infections that damage the lymphatic system. In some cases, it’s inherited. It tends to affect one limb and worsens gradually over months or years. Early treatment with compression garments and specialized massage can slow progression significantly.
Medications That Cause Swelling
Certain medications are well-known culprits. Blood pressure drugs called calcium channel blockers are among the most common offenders. The swelling is dose-related: at low doses, it affects 1 to 15% of people, but at high long-term doses, the rate can exceed 80%. These drugs work by relaxing blood vessels, which allows more fluid to leak into the tissues of the lower legs.
Other medications that frequently cause foot swelling include:
- Anti-inflammatory painkillers (NSAIDs) like ibuprofen and naproxen, which cause the kidneys to retain sodium and water
- Diabetes medications in certain classes that promote fluid retention
- Steroids like prednisone, especially with prolonged use
- Hormone therapies including estrogen and testosterone
If you notice new foot swelling after starting a medication, that timing is an important clue. Switching to a different drug within the same class can sometimes resolve the problem.
Pregnancy-Related Swelling
Some degree of foot swelling is normal during pregnancy, especially in the third trimester. Your blood volume increases by nearly 50%, and the growing uterus puts pressure on the veins returning blood from your legs. Gradual, mild swelling in both feet that comes and goes is usually nothing to worry about.
What’s not normal is sudden swelling, particularly in the face and hands. This pattern can signal preeclampsia, a serious pregnancy complication involving high blood pressure. Sudden weight gain alongside new swelling is another warning sign. Preeclampsia typically develops after 20 weeks and requires medical monitoring because it can affect both the mother’s organs and the baby’s blood supply.
Everyday Causes
Not all foot swelling has a medical cause. Sitting for long periods, like during a flight or a desk job, slows blood return from your legs and causes temporary pooling. Standing all day has a similar effect. Eating a very salty meal can cause your body to retain extra water, and that fluid tends to settle in the feet. Hot weather widens blood vessels in the legs, making it easier for fluid to seep into surrounding tissue.
Injuries are another obvious cause. A sprained ankle, a stress fracture, or even a bad bruise triggers inflammation that brings extra fluid to the damaged area as part of the healing process. This type of swelling is localized, often painful, and usually tied to a specific event you can remember.
Reducing Swelling at Home
For mild or occasional swelling, elevating your legs above heart level for about 15 minutes, three to four times a day, helps fluid drain back toward your center. Lying on a couch with your feet propped on pillows or resting them against a wall both work well. The key is getting your feet genuinely above the level of your heart, not just propped on an ottoman.
Compression socks apply gentle pressure that helps your veins push blood upward more effectively. They work best if you put them on first thing in the morning before swelling has a chance to build. Reducing salt intake helps if fluid retention is the issue, and regular movement, even brief walks or calf raises, activates the muscle pump in your legs that assists blood flow back to the heart.
Persistent swelling that doesn’t improve with elevation, swelling that appeared suddenly, or swelling in just one leg warrants a medical evaluation. The combination of swelling with skin changes, pain, warmth, or shortness of breath shifts the urgency higher.