Swollen feet happen when fluid leaks out of tiny blood vessels and gets trapped in the surrounding tissue. This is called edema, and it can result from something as simple as sitting too long or as serious as heart or kidney disease. The cause depends on whether the swelling is in one foot or both, how quickly it appeared, and what other symptoms come with it.
How Fluid Ends Up Trapped in Your Feet
Your capillaries, the smallest blood vessels in your body, constantly filter fluid outward into surrounding tissue and reabsorb it back in. Two opposing forces control this exchange: the pressure of blood pushing fluid out through vessel walls, and proteins in your blood pulling fluid back in. When these forces fall out of balance, more fluid escapes than returns, and it pools in the lowest point gravity can take it: your feet and ankles.
Several things can tip that balance. If blood pressure inside the veins rises (from standing all day, for example), more fluid gets pushed out. If protein levels in the blood drop (from kidney or liver disease), less fluid gets pulled back in. And if the lymphatic system, which acts as a drainage network for excess fluid, becomes blocked or damaged, fluid simply has nowhere to go. Nearly every cause of swollen feet traces back to one of these three disruptions.
Heart, Kidney, and Liver Disease
When the heart can’t pump blood efficiently, as in congestive heart failure, blood backs up in the veins of the legs, ankles, and feet. That backup raises pressure inside the veins, forcing fluid into the surrounding tissue. The swelling is typically worst at the end of the day and in both feet equally.
Kidney disease causes a different problem. Damaged kidneys can’t filter excess fluid and salt from the blood efficiently, so both accumulate. The resulting swelling usually shows up in the legs and around the eyes. A specific type of kidney damage called nephrotic syndrome also causes the body to lose protein through urine. With less protein in the blood, there’s less pull to draw fluid back into the capillaries, and swelling worsens.
Liver cirrhosis disrupts protein production in a similar way. The liver makes albumin, the main protein responsible for keeping fluid inside blood vessels. When the liver is scarred and failing, albumin levels drop, and fluid builds up in both the abdomen and the legs.
Vein Problems and Blood Clots
Chronic venous insufficiency affects about 1 in 20 adults. The veins in your legs contain one-way valves that push blood upward toward the heart. When those valves weaken or become damaged, blood flows backward and pools in the lower legs, a process called venous reflux. The sustained pressure stretches vein walls and forces fluid into surrounding tissue. Over time, the skin may darken, thicken, or develop ulcers near the ankle. Each year, roughly 1 in 50 adults with varicose veins progress to this condition.
A more urgent concern is deep vein thrombosis (DVT), a blood clot that forms in a deep vein, usually in one leg. Unlike most other causes, DVT tends to cause swelling in only one foot or leg. Other signs include cramping or soreness that starts in the calf, skin that turns red or purple, and warmth over the affected area. DVT is dangerous because the clot can break loose and travel to the lungs, causing a pulmonary embolism. Sudden shortness of breath, chest pain that worsens when you breathe deeply, a rapid pulse, or coughing up blood after leg swelling are emergency symptoms.
Pregnancy Swelling vs. Preeclampsia
Some degree of foot swelling is normal during pregnancy, especially in the third trimester. The growing uterus puts pressure on pelvic veins, slowing blood return from the legs. Hormonal changes also make blood vessel walls more permeable.
Preeclampsia is the version that requires medical attention. It develops after 20 weeks of pregnancy and involves high blood pressure (140/90 mm Hg or higher) along with at least one additional sign: protein in the urine, low platelet count, elevated liver enzymes, fluid in the lungs, persistent headaches that don’t respond to pain medication, or new vision disturbances. Sudden, severe swelling in the feet and hands, especially when paired with headache or visual changes, warrants prompt evaluation.
Lymphedema
When the lymphatic drainage system is damaged or blocked, protein-rich fluid accumulates in the tissue and triggers chronic inflammation and scarring. This condition, called lymphedema, produces a distinctive type of swelling that feels firmer than regular edema and doesn’t resolve with elevation alone.
One simple way to distinguish lymphedema from other types of swelling involves the skin on top of the toes. Try gently pinching and lifting the skin over the base of the second toe. If the skin lifts easily, lymphedema is less likely. If the skin feels thick and can’t be pinched, that’s a positive Stemmer sign, a hallmark of lymphedema. The thickening happens because stagnant lymph fluid causes the tissue to remodel and become fibrotic over time. Lymphedema can develop after surgery that removes lymph nodes (common in cancer treatment), after radiation, or from infections that scar the lymphatic channels.
Everyday Causes
Not all foot swelling signals disease. Prolonged sitting or standing lets gravity pull fluid downward, and without movement to activate the calf muscles that pump blood back up, swelling builds. Long flights, desk jobs, and extended car rides are common triggers. Hot weather makes it worse because heat causes blood vessels to widen, allowing more fluid to escape.
High sodium intake plays a significant role. Salt causes the body to retain water, increasing blood volume and the pressure that pushes fluid into tissue. For people already prone to swelling, cardiology guidelines from multiple international organizations converge on keeping sodium below 2,000 mg per day, roughly the amount in one teaspoon of table salt. The average diet contains well over that.
Certain medications also cause fluid retention as a side effect. Calcium channel blockers (used for blood pressure), some diabetes medications, steroids, and nonsteroidal anti-inflammatory drugs like ibuprofen are frequent culprits. The swelling is usually in both feet and often improves if the medication is adjusted.
When Swelling Affects Only One Foot
Bilateral swelling (both feet) generally points to a systemic cause: heart, kidney, or liver problems, medication side effects, or prolonged inactivity. Unilateral swelling (one foot) narrows the possibilities significantly. The most common causes are DVT, a localized infection, injury, or lymphedema affecting one limb. One-sided swelling that appears suddenly, with pain and skin color changes, should be evaluated quickly to rule out a blood clot.
Reducing Swelling at Home
Elevation is the simplest intervention. Raising your legs to just above the level of your heart while lying down or reclining lets gravity work in reverse, helping fluid drain back toward your core. Doing this for 20 to 30 minutes several times a day can make a noticeable difference, though the specific duration needed hasn’t been precisely established in clinical studies.
Compression stockings apply graduated pressure to the legs, tightest at the ankle and looser toward the knee, to help push fluid upward. They come in three general pressure ranges: low (under 20 mmHg), medium (20 to 30 mmHg), and high (above 30 mmHg). Low compression is usually sufficient for mild, activity-related swelling. Medium and high compression are typically used for chronic venous insufficiency or lymphedema and may require a fitting to ensure they work properly without restricting circulation.
Movement matters as much as any other strategy. Walking, flexing your ankles, and rising onto your toes all engage the calf muscles, which act as a pump to push blood out of the lower legs. If you sit for long stretches, even small ankle circles under your desk help. Cutting back on sodium, staying hydrated (which paradoxically helps the body release excess fluid rather than hold onto it), and maintaining a healthy weight all reduce the baseline pressure that drives swelling in the first place.