Swollen feet happen when fluid gets trapped in the tissues of your lower extremities, and the causes range from something as simple as sitting too long to something as serious as heart or kidney disease. The medical term is edema, and it’s the most common in the feet, ankles, and legs because gravity pulls fluid downward throughout the day. Figuring out why your feet are swollen depends on whether the swelling is new or ongoing, affects one foot or both, and whether you have other symptoms alongside it.
How Fluid Ends Up in Your Feet
Your blood vessels constantly filter small amounts of fluid out into surrounding tissues and then reabsorb most of it back. Normally, only about 1% of plasma leaks out, and your lymphatic system picks up the excess. Swelling happens when that balance tips: either too much fluid is being pushed out, not enough is being pulled back in, or your lymphatic drainage can’t keep up.
Several things can shift that balance. Higher blood pressure inside the veins (from standing all day, for example) forces more fluid out. Inflammation from an injury or infection makes blood vessel walls “leakier,” letting fluid pour into tissues faster than usual. And conditions that lower protein levels in your blood, like kidney or liver disease, reduce the pulling force that normally draws fluid back into your vessels.
The Most Common Everyday Causes
If your swelling comes and goes and you’re otherwise feeling fine, one of these is the likely culprit:
- Prolonged sitting or standing. Long stretches without moving your legs let fluid pool in your feet. This is especially common during flights, desk jobs, or road trips.
- High sodium intake. Salt causes your body to hold onto water. Processed meats, canned soups, fast food, chips, and cheese are common sources. For people prone to swelling, keeping sodium below about 1,500 to 1,800 mg per day often makes a noticeable difference.
- Heat. Warm weather dilates blood vessels, making it easier for fluid to seep into tissues.
- Alcohol. Overuse contributes to fluid retention both directly and by stressing the liver over time.
- Medication side effects. Blood pressure medications (particularly calcium channel blockers), hormone therapies, steroids, and some diabetes drugs are known to cause foot and ankle swelling.
Medical Conditions That Cause Swelling
When swollen feet persist, worsen over time, or show up alongside other symptoms, an underlying health condition may be at play.
Heart Failure
A weakening heart can’t pump blood forward efficiently, so pressure builds up in the veins and fluid backs into the legs. Sudden worsening of swelling in both legs is one of the most common reasons people with heart failure end up in the emergency department. You might also notice shortness of breath, fatigue, or swelling that’s worse at the end of the day.
Kidney Disease
Your kidneys regulate how much fluid and sodium stay in your body. When they’re not working well, excess fluid accumulates. Kidney-related swelling often affects the feet and ankles but can also show up around the eyes, especially in the morning.
Liver Disease
The liver produces albumin, the main protein that keeps fluid inside your blood vessels. Liver damage reduces albumin levels, and fluid leaks into tissues more easily. Swollen feet combined with a distended abdomen can point toward liver problems.
Thyroid Disease
An underactive thyroid slows metabolism and can lead to a specific type of swelling that feels firm and doesn’t leave an indent when you press on it. This is different from most other causes of puffy feet.
Sleep Apnea
Repeated drops in oxygen during sleep can strain the right side of the heart over time, leading to fluid buildup in the legs. If you snore heavily and wake up with swollen feet, the two may be connected.
One Foot vs. Both Feet Matters
Whether one foot is swollen or both gives an important clue about the cause. Swelling in both feet usually points to something systemic: a medication, too much salt, or an organ issue like heart, kidney, or liver disease. Swelling in just one foot is more likely a local problem, and it needs a different kind of attention.
The most serious cause of sudden one-sided swelling is 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, or pain in the calf. A DVT requires urgent medical evaluation because the clot can break loose and travel to the lungs. If one leg swells up suddenly, especially after surgery, a long flight, or a period of immobility, get it checked promptly.
The most common cause of chronic one-sided swelling is venous insufficiency, where the valves in leg veins weaken and blood pools instead of flowing back up to the heart. Over time, this can cause visible skin changes: yellowish-brown discoloration around the ankles, red or scaly patches, itching, and tenderness. Left untreated, venous insufficiency can lead to open sores on the lower legs that are slow to heal.
Swollen Feet During Pregnancy
Some swelling in the feet and ankles is a normal part of pregnancy, especially in the third trimester, as the growing uterus puts pressure on veins returning blood from the legs. Ankle swelling alone is generally considered normal.
What isn’t normal is sudden, significant swelling of the hands, arms, or face, particularly when it comes with a spike in blood pressure. This pattern can signal preeclampsia, a serious pregnancy complication defined by blood pressure at or above 140/90 along with protein in the urine. Severe preeclampsia can also cause headaches, vision changes, nausea, upper abdominal pain, and difficulty breathing. If swelling during pregnancy feels sudden, involves your hands or face, or comes with any of those symptoms, it needs immediate evaluation.
How to Check the Severity
You can get a rough sense of how significant your swelling is with a simple test. Press your thumb firmly into the swollen area for about five seconds, then release and watch what happens. If the skin bounces back immediately and the indent is barely visible (about 2 mm), the swelling is mild. If the indent is deeper and takes 15 to 60 seconds to fill back in, it’s moderate. In severe cases, the pit can be 8 mm deep and take two to three minutes to rebound.
This “pitting” test is what doctors use to grade edema on a 1-to-4 scale. If you’re noticing deep pits that take a long time to fill in, that’s a sign the swelling is more than a minor nuisance.
Reducing Swelling at Home
For mild, everyday swelling, a few habits can make a real difference:
Elevate your legs. Lie down and prop your feet above the level of your heart for about 15 minutes, three to four times a day. This uses gravity to drain fluid back toward your core. A couple of pillows under your calves while lying on the couch works well.
Move regularly. If you sit or stand for long stretches, take breaks to walk around or flex your calves. The muscle contractions in your lower legs act as a pump, pushing fluid upward through your veins.
Cut back on sodium. Read labels and aim to stay under 1,800 mg of sodium per day if swelling is a recurring problem. Restaurant and packaged foods are the biggest sources for most people.
Try compression stockings. Mild compression (8 to 15 mmHg) is available over the counter and works well for minor swelling, tired legs, and preventive use during travel. If you have chronic venous insufficiency or more severe edema, firmer compression (30 to 40 mmHg) is more effective but should be used with medical guidance to make sure the fit and pressure level are right for your situation.
When Swelling Signals Something Serious
Most swollen feet are a nuisance, not an emergency. But certain patterns deserve prompt attention: sudden swelling in one leg (especially with warmth, redness, or calf pain), swelling that gets worse rapidly over days, swelling paired with shortness of breath or chest pain, or pregnancy swelling that spreads to the hands and face. Persistent swelling that doesn’t improve with elevation and salt reduction is also worth discussing with a doctor, as it may be the first visible sign of a heart, kidney, or liver issue that’s easier to manage when caught early.