Feet swell when fluid leaks out of small blood vessels and accumulates in the surrounding tissue. This can happen for reasons as simple as sitting too long or eating a salty meal, or it can signal something more serious like heart failure, vein disease, or a blood clot. Understanding the pattern of your swelling, whether it affects one foot or both, and what other symptoms accompany it can help narrow down the cause.
How Fluid Ends Up in Your Feet
Your body constantly moves fluid between your bloodstream and your tissues. Two forces keep this exchange balanced: pressure inside the blood vessels pushes fluid out, while proteins (especially one called albumin) pull fluid back in. When something disrupts this balance, fluid escapes faster than it can be reabsorbed, and gravity pulls it down to your feet and ankles.
Once swelling starts, the kidneys often make things worse. They sense the fluid shift as a drop in blood volume and respond by holding onto more sodium and water, which adds even more fluid to the system. This is why swelling from many different causes tends to follow a similar cycle: fluid leaks out, the body compensates by retaining more, and the swelling builds.
One Foot vs. Both Feet
Whether your swelling is in one foot or both is one of the most important clues to its cause. Swelling in both feet typically points to a systemic issue: heart problems, kidney disease, medication side effects, or prolonged sitting or standing. Swelling in just one foot is a different story. Acute swelling in a single leg is most commonly caused by a blood clot (deep vein thrombosis) or an injury. If one leg suddenly swells and feels warm, tender, or red, that warrants urgent medical attention because a clot can travel to the lungs.
Chronic swelling in one leg is often due to venous insufficiency or lymphedema, though in rarer cases it can indicate a blockage from something like a tumor pressing on a vein or lymph channel.
Venous Insufficiency
The most common cause of persistent leg and foot swelling is chronic venous insufficiency, which affects roughly 1 in 20 adults. Your leg veins contain one-way valves that help push blood upward against gravity toward your heart. When those valves become damaged, blood flows backward and pools in the lower legs. The resulting pressure forces fluid into the surrounding tissue.
Over time, venous insufficiency can cause skin changes around the ankles, including darkening, thickening, and a type of eczema called stasis dermatitis. The swelling is usually worse after long periods of standing and improves overnight when your legs are elevated. Risk factors include obesity, pregnancy, a history of blood clots, and jobs that require extended standing.
Heart, Kidney, and Liver Problems
When the heart can’t pump blood efficiently, blood backs up in the veins, and pressure builds in the small vessels of the legs. Fluid leaks into the tissues, causing swelling that typically worsens throughout the day and may be accompanied by shortness of breath, persistent coughing, or fatigue. The shortness of breath happens because fluid also backs up into the lungs.
Kidney disease causes swelling differently. Damaged kidneys lose their ability to filter sodium and water properly, so excess fluid accumulates throughout the body. You may notice puffiness around the eyes in the morning in addition to swollen feet later in the day. Liver disease, particularly cirrhosis, reduces production of albumin, the protein that keeps fluid inside blood vessels. When albumin drops too low, fluid seeps into tissues throughout the body, including the feet and abdomen.
Medications That Cause Swelling
Several common medications cause foot swelling as a side effect, and many people don’t realize their prescription is the culprit. The most well-known offenders are calcium channel blockers, a class of blood pressure medications. These drugs widen arteries but not veins, creating an imbalance that increases pressure in the smallest blood vessels and pushes fluid into surrounding tissue. The more potent the medication, the more likely it is to cause swelling. Amlodipine, one of the most widely prescribed blood pressure drugs, is a frequent cause.
Anti-inflammatory pain relievers like ibuprofen and naproxen can also trigger swelling by causing the kidneys to retain sodium and water. Other medications linked to foot edema include certain diabetes drugs, some antidepressants, steroids, and blood vessel-widening drugs like minoxidil and hydralazine. If you notice new swelling after starting a medication, it’s worth discussing with your prescriber. The swelling from these drugs rarely goes away on its own without a dose change or switch to a different medication.
Lymphedema
Lymphedema is a distinct type of swelling caused by a problem with the lymphatic system, the network of vessels that drains excess fluid from tissues and returns it to the bloodstream. Unlike swelling from heart or vein problems, where the lymphatic system is overwhelmed by too much fluid, lymphedema happens when the lymphatic system itself is damaged or underdeveloped and can’t keep up with normal fluid levels.
It typically starts in one foot or leg and progresses from the toes upward. Early on, the swelling is soft and you can press a dent into it. Over months or years, the tissue becomes firmer and the skin thickens. One classic sign is the inability to pinch the skin at the base of the second toe, known as the Stemmer sign. Common causes include cancer treatment that removed or damaged lymph nodes, radiation therapy, infections, and in some cases genetic conditions present from birth. Many people also develop a combination of venous insufficiency and lymphatic damage, sometimes called phlebolymphedema, where high pressure in the veins gradually overloads and damages the lymphatic system.
Pregnancy-Related Swelling
Mild foot and ankle swelling is extremely common during pregnancy, especially in the third trimester. The growing uterus puts pressure on pelvic veins, slowing blood return from the legs, and hormonal changes cause the body to retain more fluid. This type of swelling is usually gradual and affects both feet.
What requires attention is swelling that comes on suddenly, is painful, or appears in the face and hands. Sudden worsening of swelling can be a sign of preeclampsia, a pregnancy complication involving high blood pressure that can become dangerous. Painful swelling in just one leg raises concern for a blood clot, which is more common during pregnancy. Any rapid change in swelling pattern during pregnancy should be evaluated promptly.
Everyday Causes
Not all foot swelling signals a medical problem. Sitting or standing for hours at a time, whether on a long flight, at a desk, or during a shift on your feet, reduces circulation and allows fluid to pool. Hot weather dilates blood vessels and makes leakage more likely. A high-sodium meal can trigger noticeable fluid retention within hours. The American Heart Association recommends staying under 1,500 mg of sodium daily, though the average person consumes well over double that. Cutting back on processed foods, canned soups, and restaurant meals is the most practical way to reduce sodium-related swelling.
Reducing and Managing Swelling
Elevating your feet above the level of your heart for 20 to 30 minutes several times a day is one of the simplest and most effective ways to reduce swelling from most causes. This lets gravity work in your favor, helping fluid drain back into circulation.
Compression stockings apply graduated pressure that supports your veins and prevents fluid from pooling. For preventing swelling during long workdays, stockings rated at 15 to 20 mmHg are effective for most people. Those with more significant swelling or venous insufficiency often benefit from 20 to 30 mmHg compression. Research shows that even light compression in the 10 to 15 mmHg range can meaningfully reduce swelling in people who stand or sit for extended periods. People who sit most of the day tend to see greater benefit from the higher 20 to 30 mmHg range.
Regular movement matters too. Walking activates the calf muscles, which act as a pump to push blood back up through the veins. If you’re desk-bound, flexing your ankles up and down periodically throughout the day mimics some of this pumping action. Reducing sodium intake, staying hydrated, and maintaining a healthy weight all help lower baseline fluid retention.
Symptoms That Signal an Emergency
Foot swelling combined with shortness of breath, chest pain, or a cough producing pink or bloody mucus can indicate heart failure or a pulmonary embolism and requires emergency care. Sudden, painful swelling in one leg with warmth and redness suggests a possible blood clot. Swelling that comes on rapidly during pregnancy alongside headache, vision changes, or upper abdominal pain points toward preeclampsia. In each of these situations, the swelling itself isn’t the danger, but it’s a visible warning of something happening internally that needs immediate attention.