Feet swell when fluid that normally stays inside your blood vessels leaks out into the surrounding tissue. This happens because of a pressure imbalance: your capillaries are constantly filtering fluid outward, and your body is constantly pulling it back in. When something tips that balance, whether it’s gravity, a health condition, or a medication, fluid accumulates in the lowest point it can find, which is usually your feet and ankles.
How Fluid Ends Up in Your Feet
Your smallest blood vessels, the capillaries, aren’t sealed tubes. They’re slightly porous, and fluid constantly moves through their walls in both directions. Two main forces control this exchange: the pressure of blood pushing fluid out, and the pulling force of proteins (especially albumin) in your blood drawing fluid back in. At the same time, your lymphatic system acts like a drainage network, picking up excess fluid from tissues and returning it to your bloodstream.
Swelling develops when one or more of these systems fails. The blood pressure inside your capillaries might rise too high, pushing more fluid out than usual. Your blood might not contain enough protein to pull fluid back in. Your lymphatic drainage might be blocked. Or your capillary walls might become more permeable during inflammation, letting fluid pour through faster than it can be reabsorbed. Often, more than one of these problems occurs at the same time.
Gravity does the rest. Because your feet sit at the bottom of your body, leaked fluid naturally pools there. This is why foot swelling tends to worsen throughout the day and improve overnight when you’re lying flat.
Sitting and Standing Too Long
The most common reason for foot swelling in otherwise healthy people is simply staying in one position for too long. Your calf muscles act as a pump for your veins, squeezing blood upward toward your heart with every step. When you sit at a desk for hours or stand in one spot, that pump goes idle, and blood pools in your lower legs. The increased pressure in your leg veins forces more fluid into the surrounding tissue.
Research comparing uninterrupted sitting to periodic movement found that even 20 minutes of continuous sitting causes measurable fluid expansion in the lower legs. Breaking up sitting time with brief standing or walking intervals significantly reduces this effect. The fix is straightforward: if your job keeps you in one position, set a reminder to move every 20 to 30 minutes. Even small shifts like flexing your ankles or doing a few calf raises help activate the muscle pump.
Vein Problems in the Legs
Your leg veins contain one-way valves that keep blood moving upward against gravity. In chronic venous insufficiency, those valves become damaged and can’t close properly. Blood falls backward, pools in the lower legs, and the sustained pressure causes persistent swelling. Over time, this can also lead to skin changes and ulcers around the ankles.
Several things can damage these valves. A previous deep vein thrombosis (a blood clot in a deep leg vein) is one of the most common culprits. The clot leaves behind scar tissue that prevents the valve from sealing. Some people are born with veins that are too wide for their valves to close completely, and others are born without certain valves altogether. Venous insufficiency tends to develop gradually and worsen over years, so swelling that started mild and has slowly become a daily problem is a characteristic pattern.
Heart, Kidney, and Liver Conditions
When the heart can’t pump blood efficiently, as in congestive heart failure, blood backs up in the veins. This raises pressure in the leg veins the same way a clogged drain raises the water level in a sink. The result is swelling in the feet, ankles, and lower legs that tends to worsen as the day goes on and may leave a visible dent when you press on the skin.
Kidney disease contributes to swelling through a different route. Damaged kidneys may lose protein into the urine, lowering the concentration of albumin in your blood. Since albumin is the main protein responsible for pulling fluid back into your blood vessels, less of it means fluid stays trapped in the tissues. Liver disease, particularly cirrhosis, causes the same problem because the liver is where albumin is made. When production drops, the pulling force inside your capillaries weakens, and fluid leaks out throughout the body, settling in the feet and abdomen.
Any inflammatory condition can also make capillary walls more permeable. When that happens, both fluid and proteins escape into the tissues faster than the lymphatic system can clear them. The proteins that leak out actually trap more water in the tissue, making swelling worse.
Medications That Cause Swelling
Certain blood pressure medications are well known for causing foot and ankle swelling. Calcium channel blockers, a class of drugs commonly prescribed for high blood pressure and chest pain, work by relaxing blood vessel walls. They dilate arteries more than veins, which increases the pressure difference across capillaries and pushes fluid out. Reported rates of swelling with these medications range from 5% to as high as 70%, depending on the dose. The swelling tends to get worse at higher doses.
Anti-inflammatory painkillers like ibuprofen and naproxen can also cause fluid retention by affecting how your kidneys handle sodium and water. If you’ve noticed new foot swelling after starting any medication, it’s worth checking whether edema is a listed side effect.
Pregnancy and Hormonal Changes
Some degree of foot swelling is normal during pregnancy, especially in the third trimester. The growing uterus puts pressure on the large veins that return blood from the legs, and hormonal shifts increase blood volume and relax blood vessel walls. Most pregnancy-related swelling is harmless, though uncomfortable.
The exception is preeclampsia, a serious condition marked by high blood pressure and organ damage. One of its warning signs is sudden swelling of the face, hands, or feet, which is distinct from the gradual swelling that builds over weeks. Sudden or severe swelling during pregnancy, especially paired with headaches, vision changes, or upper abdominal pain, requires immediate medical attention. Hormonal fluctuations outside of pregnancy, including those tied to the menstrual cycle and menopause, can also cause mild, temporary fluid retention in the feet and ankles.
One Foot vs. Both Feet
Whether one foot or both feet are swollen tells you a lot about the likely cause. As a general rule, swelling in both feet points to a systemic problem: heart failure, kidney disease, medication side effects, or prolonged inactivity. Swelling in just one foot suggests something local is going on, such as an injury, infection, a blood clot, gout, or a blockage in the lymphatic drainage on that side.
Rapid-onset swelling in one leg, particularly if it’s painful, warm, or red, raises concern for deep vein thrombosis. A clot that develops quickly can cause noticeable swelling within 72 hours. This is the scenario where prompt evaluation matters most, because a clot in a deep leg vein can break loose and travel to the lungs.
Reducing Everyday Swelling
For swelling caused by long hours on your feet or at a desk, the simplest intervention is elevation. Raising your feet above heart level for 15 to 20 minutes helps gravity drain fluid back toward your core. Doing this a few times a day, especially in the evening, can make a noticeable difference.
Compression stockings provide a more sustained solution. Research shows that light compression (10 to 15 mmHg) is effective at preventing occupational swelling in people who sit or stand for long stretches. Stockings in the 15 to 20 mmHg range produced significant reductions in leg swelling compared to no compression, and 20 to 30 mmHg stockings performed even better, particularly for people who sit most of the day. Knee-high styles are typically sufficient for foot and ankle swelling. You don’t need a prescription for the lighter pressure levels.
Regular movement is the other key piece. Walking, cycling, swimming, or any activity that engages your calf muscles improves venous return and helps prevent fluid from pooling. Even on days when extended exercise isn’t possible, frequent short walks and ankle rotations keep the muscle pump working.
Reducing sodium intake is commonly recommended, though the relationship between salt and swelling is more nuanced than often presented. A controlled study found that healthy adults on very high sodium diets didn’t develop measurable fluid retention or visible edema. The effect of salt on swelling appears to be more significant in people who already have compromised heart, kidney, or liver function, where the body’s ability to excrete excess sodium is impaired. For those individuals, limiting sodium can meaningfully reduce fluid buildup.