Swollen feet happen when fluid leaks out of tiny blood vessels and collects in the surrounding tissue. This is called edema, and it ranges from harmless (you stood all day) to a signal that something in your heart, kidneys, liver, or veins needs attention. The cause usually falls into one of a handful categories, and the pattern of swelling, along with any other symptoms, is the biggest clue to which one.
Why Fluid Builds Up in Your Feet
Your blood vessels constantly balance two opposing forces: pressure pushing fluid out into surrounding tissue, and proteins in your blood pulling fluid back in. When something tips that balance, fluid escapes faster than your body can reabsorb it, and gravity pulls it downward into your feet and ankles.
Five things can shift that balance: higher pressure inside the blood vessels (from standing, heart problems, or blocked veins), lower protein levels in the blood (from kidney or liver disease), damage to the vessel walls that lets fluid leak through, a buildup of waste products in the tissue that draws fluid toward them, and a backup in the lymphatic system that normally drains excess fluid away. Most causes of swollen feet trace back to one or more of these mechanisms.
Standing or Sitting Too Long
The most common and least worrying cause is simply being on your feet or sitting in one position for hours. When your legs stay below your heart for a long time without much movement, blood pools in the veins of your lower legs. That raises the pressure inside those veins, which pushes fluid out into the surrounding tissue. Long flights, desk jobs, and shifts where you stand in one spot are classic triggers. The swelling is usually mild, affects both feet equally, and goes down after you lie down or elevate your legs.
Chronic Venous Insufficiency
Your leg veins have one-way valves that push blood upward against gravity. When those valves weaken or stop working properly, blood flows backward and pools in the lower legs. This condition, chronic venous insufficiency, is one of the most common causes of persistent foot and ankle swelling.
Early on, you might notice swelling that worsens throughout the day and improves overnight. Over time, other signs develop: varicose veins, a heavy or achy feeling in your legs, skin that turns reddish-brown around the ankles, itching or flaking skin, and in advanced cases, open sores near the ankles. Clinicians grade venous disease on a scale from stage 0 (symptoms but nothing visible) up through stage 6 (active ulcers). Swelling without skin changes falls around stage 3. If you’re seeing skin discoloration or texture changes, the condition has progressed further.
Heart Failure
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 forces fluid into the tissues. Heart failure typically causes swelling in both ankles and lower legs, and it often comes with other symptoms: shortness of breath (especially lying flat), fatigue, rapid weight gain from fluid retention, and visible swelling in the neck veins. Swelling in the belly can also occur as fluid accumulates in the abdomen.
If your feet are swelling and you’re also winded doing things that used to be easy, or you’ve gained several pounds in just a few days, heart function should be evaluated.
Kidney and Liver Problems
Your blood relies on a protein called albumin to pull fluid back into the vessels. Both the kidneys and the liver play a role in keeping albumin levels normal, and when either organ falters, swelling follows.
In kidney disease, especially a condition called nephrotic syndrome, damaged filters in the kidneys let protein spill into the urine instead of keeping it in the blood. With less protein in the bloodstream, fluid leaks into the tissue. Kidney-related swelling often shows up in both the legs and around the eyes.
Liver disease works differently but produces a similar result. A damaged liver can’t manufacture enough albumin. Cirrhosis commonly causes fluid buildup in the abdomen (a condition called ascites) along with swelling in the legs.
Medications That Cause Swelling
Several widely prescribed drugs cause foot swelling as a side effect. The most well-known culprits are a class of blood pressure medications called calcium channel blockers (amlodipine is one of the most common). Between 1% and 15% of people taking standard doses develop ankle swelling, and at high doses over a long period, the rate can exceed 80%. Adding a second type of blood pressure medication (an ACE inhibitor or ARB) to the regimen cuts swelling episodes by roughly 38%.
Other medications that frequently cause fluid retention include anti-inflammatory painkillers (ibuprofen, naproxen), certain diabetes drugs, steroids like prednisone, and some hormone therapies including estrogen. If your swelling started or worsened after beginning a new medication, that connection is worth raising with your prescriber.
Pregnancy-Related Swelling
Mild foot swelling during pregnancy is extremely common, especially in the third trimester, because increased blood volume and pressure from the uterus slow the return of blood from the legs. This kind of swelling is usually harmless.
What’s not normal is sudden, severe swelling after 20 weeks of pregnancy, especially if it comes with a headache that won’t respond to pain relievers, vision changes, or upper abdominal pain. These are warning signs of preeclampsia, which is diagnosed when blood pressure reaches 140/90 or higher along with signs of organ stress such as protein in the urine, low platelet counts, or elevated liver enzymes. Preeclampsia requires prompt medical evaluation.
Blood Clots: When One Foot Swells
Swelling that appears suddenly in just one leg is a red flag for a deep vein thrombosis (DVT), a blood clot in one of the deep veins of the leg. Along with swelling, you might notice warmth, redness, and pain or tenderness in the calf or thigh. The risk is higher if you’ve recently had surgery, been immobile for days, traveled a long distance, have active cancer, or have had a DVT before.
A useful clinical rule: if the swollen calf measures more than 3 centimeters larger than the other calf, and you have tenderness along the vein plus one or two risk factors, the probability of a clot is moderate to high. DVT can be dangerous if a piece of the clot breaks off and travels to the lungs, so one-sided leg swelling with pain warrants urgent evaluation.
Salt, Weight, and Other Lifestyle Factors
High sodium intake is one of the most controllable contributors to swelling. Sodium causes your body to hold onto water, increasing blood volume and the pressure inside your vessels. Most adults consume well above the recommended limit. Cutting back on processed foods, restaurant meals, and added salt can noticeably reduce mild edema within days to weeks.
Excess body weight adds to the problem by increasing pressure on the veins in the pelvis and legs, slowing blood return to the heart. Heat also plays a role: in warm weather, blood vessels near the skin dilate to release heat, and this can allow more fluid to seep into the tissue.
What You Can Do at Home
For mild, everyday swelling, a few strategies make a real difference. Elevating your legs above heart level for about 15 minutes, three to four times a day, uses gravity to drain fluid back toward your core. Moving regularly matters too: calf muscles act as pumps that push blood upward through the veins, so walking, ankle circles, or simply flexing your feet while sitting can help prevent fluid from pooling.
Compression socks provide graduated pressure that supports your veins. For mild swelling, over-the-counter socks rated at 15 to 20 mmHg are a good starting point. Moderate edema or varicose veins respond better to 20 to 30 mmHg. Higher levels (30 to 40 mmHg and above) are typically prescription-strength and used for lymphedema or chronic venous insufficiency. Start with lighter compression and move up if needed.
Reducing sodium, staying hydrated, and maintaining a healthy weight round out the basics. These measures won’t fix swelling caused by a serious underlying condition, but they help with the common, gravity-related kind and can complement medical treatment when something more is going on.
Patterns That Point to the Cause
A few details can help you and your doctor narrow things down quickly. Swelling in both feet that worsens with standing and improves overnight points toward venous insufficiency, prolonged positioning, or a systemic cause like heart, kidney, or liver issues. Swelling in just one leg, especially with pain, raises concern for a blood clot or a localized vein problem. Swelling that leaves a dent when you press it (called pitting edema) is typical of fluid overload from heart, kidney, or vein issues. Swelling that feels firm and doesn’t pit is more common with lymphatic problems. And if the swelling came on within weeks of starting a new medication, the drug is a likely suspect.