Foot swelling happens when excess fluid builds up in the tissues of your foot and ankle. The causes range from something as simple as standing too long to serious conditions like blood clots or heart failure. Whether one foot or both are swollen, and whether the swelling appeared suddenly or gradually, tells you a lot about what’s going on.
How Swelling Actually Happens
Your blood vessels constantly exchange fluid with surrounding tissues. Swelling occurs when that balance tips and more fluid leaks out of your capillaries than gets reabsorbed. This can happen through several mechanisms: increased pressure inside the blood vessels (from standing, gravity, or a backed-up heart), leaky vessel walls (from injury or infection), poor drainage through the lymphatic system, or low protein levels in the blood that normally pull fluid back in. Gravity makes the feet and ankles the lowest collection point for all that extra fluid.
One Swollen Foot vs. Both
This distinction matters more than most people realize. Swelling in just one foot points toward a local problem. About 40% of acute single-leg swelling cases come from muscle strains, tears, or twisting injuries. Another 7% stem from infections or blocked lymph channels, and about 5% from fluid-filled cysts behind the knee. A blood clot in a deep vein is the most important diagnosis to rule out when one leg swells suddenly without an obvious injury.
When both feet swell, the cause is more likely something systemic affecting your whole body. Chronic vein disease is the most common culprit. Heart failure, kidney disease, liver disease, and certain medications all cause fluid to pool in both legs. Hormonal shifts, including premenstrual fluid retention, can do the same. Even sleep apnea can contribute by raising pressure in the blood vessels of the lungs, which backs fluid up into the legs over time.
Medications That Cause Swelling
If your foot swelling started around the same time as a new prescription, the medication itself may be responsible. Calcium channel blockers, a common type of blood pressure drug, are one of the most frequent offenders. Nearly half of people taking these medications experience some degree of foot and ankle swelling. Amlodipine is a well-known example.
Other medications linked to foot swelling include:
- Anti-inflammatory painkillers (NSAIDs) like ibuprofen and naproxen
- Hormone treatments including corticosteroids, estrogen, progesterone, and testosterone
- Nerve pain and seizure medications like gabapentin and pregabalin
- Other blood pressure drugs including beta blockers, clonidine, and hydralazine
- The diabetes drug pioglitazone
- Certain antidepressants and Parkinson’s medications
Chronic Venous Insufficiency
Chronic venous insufficiency is the single most common cause of persistent foot and leg swelling. It happens when the one-way valves inside your leg veins stop working properly, allowing blood to flow backward and pool in your lower legs. Over time, the increased pressure forces fluid into the surrounding tissue.
The swelling from venous insufficiency tends to be worse at the end of the day or after long periods of standing, and it improves overnight when you’re lying down. Other signs include aching or heavy-feeling legs, visible varicose veins, skin that turns reddish-brown around the ankles, and itchy or flaky skin on the lower legs. In advanced cases, the skin becomes leathery and thick, and open sores (ulcers) can develop near the ankles. Diagnosis typically involves a physical exam and a painless ultrasound that shows which valves are damaged.
Swelling During Pregnancy
Some foot swelling is normal during pregnancy, especially in the third trimester. But sudden swelling, particularly in the face and hands along with the feet, can signal preeclampsia, a serious pregnancy complication involving high blood pressure.
Warning signs that go beyond normal pregnancy swelling include severe headaches, blurred vision or light sensitivity, pain in the upper belly (usually under the ribs on the right side), shortness of breath, and nausea or vomiting. Sudden, significant weight gain over a few days also warrants attention. If you experience any of these alongside rapid swelling, seek emergency care.
Red Flags That Need Urgent Attention
A deep vein thrombosis (DVT), or blood clot in a leg vein, is the most dangerous cause of sudden foot swelling. The clot itself is treatable, but the real threat is a piece breaking off and traveling to the lungs, called a pulmonary embolism. DVT typically causes swelling in one leg along with warmth, redness, and pain that can feel like a deep cramp.
Seek emergency help if you develop sudden shortness of breath, chest pain that worsens when you breathe in or cough, a rapid pulse, dizziness or fainting, or coughing up blood. These are signs a clot may have reached your lungs.
Swelling accompanied by fever, increasing redness, and skin that’s hot to the touch may indicate cellulitis, a spreading skin infection that needs prompt antibiotic treatment.
What Pitting Tells You
When you press a swollen area with your finger and it leaves a temporary dent, that’s called pitting edema. Doctors grade it on a 1 to 4 scale based on how deep the dent is and how long it takes to bounce back. A grade 1 pit is about 2 millimeters deep and rebounds immediately. A grade 4 pit is about 8 millimeters deep and takes two to three minutes to fill back in. Higher grades generally indicate more fluid buildup and a greater need to identify the underlying cause.
Reducing Swelling at Home
Elevating your legs is the simplest and most effective way to drain excess fluid. Lie down and prop your feet above the level of your heart using pillows. Aim for about 15 minutes at a time, three to four times a day. If you can’t get your feet that high, resting them on an ottoman or coffee table still helps by working against gravity.
Compression socks apply gentle, graduated pressure that helps push fluid back up toward your heart. They’re most helpful for swelling caused by venous insufficiency, prolonged standing, or long flights. Put them on in the morning before swelling builds up during the day.
Reducing sodium intake makes a meaningful difference for people with fluid retention. The general target for managing edema is no more than 2,000 to 3,000 milligrams of sodium per day, with stricter limits (under 2,000 mg) for people with moderate to severe heart failure. For reference, a single teaspoon of table salt contains about 2,300 mg. Processed foods, restaurant meals, and canned soups are the biggest sources for most people.
Regular movement helps too. Walking activates the calf muscles, which act as a pump to squeeze blood back up through your veins. If you sit or stand for long stretches, even flexing your feet up and down every 20 to 30 minutes can make a noticeable difference.