Swollen feet happen when fluid builds up in the tissue of your lower extremities, a condition called peripheral edema. The causes range from something as simple as sitting too long to something as serious as heart failure. In most cases, the swelling is temporary and harmless, but certain patterns, especially sudden or one-sided swelling, signal a problem that needs prompt medical attention.
How Fluid Ends Up in Your Feet
Your body constantly moves fluid between your bloodstream and the surrounding tissue. Two opposing forces keep things balanced: pressure inside your blood vessels pushes fluid out, while proteins (mainly albumin) in your blood pull fluid back in. Your lymphatic system acts as a cleanup crew, draining whatever excess fluid slips through.
Swelling happens when this balance breaks down. That can mean too much pressure forcing fluid out, too little protein pulling it back, leaky blood vessel walls letting fluid escape, or a sluggish lymphatic system failing to clear it. Gravity does the rest. Because your feet are the lowest point on your body, that’s where excess fluid pools first.
Your kidneys also play a role. When your body senses reduced blood flow, it responds by holding onto sodium and water. This compensatory reflex increases your total fluid volume, which can make swelling worse over time.
Common Everyday Causes
Most foot swelling isn’t caused by a disease. Long periods of sitting or standing are the most frequent culprits. When your calf muscles aren’t contracting, they can’t pump blood back up toward your heart efficiently, and fluid settles downward. Hot weather makes this worse because your blood vessels widen to release heat, allowing more fluid to seep into surrounding tissue.
High sodium intake is another major contributor. The more salt you consume, the more water your kidneys retain. Shoes that are too tight, carrying extra body weight, or simply being on your feet all day at work can all amplify the problem. For many people, the swelling appears in the evening and resolves overnight once they lie down.
Medications That Cause Swelling
Several common medications trigger foot swelling through different mechanisms. Some cause your kidneys to retain sodium and water. Others widen your arteries, increasing blood flow to tiny capillaries and pushing more fluid into surrounding tissue. Blood pressure medications called calcium channel blockers are well known for this side effect. Anti-inflammatory drugs, certain diabetes medications, and hormone therapies (including estrogen and testosterone) can also cause noticeable swelling. If your feet started swelling after beginning a new medication, that connection is worth discussing with your prescriber.
Chronic Venous Insufficiency
Chronic venous insufficiency, or CVI, is one of the most common medical causes of persistent foot and leg swelling. It affects an estimated 10% to 35% of adults in the United States. The condition develops when the valves inside your leg veins weaken or fail, allowing blood to flow backward and pool in the lower legs instead of returning to the heart.
Early on, CVI shows up as pitting edema (swelling that holds a thumbprint indentation when you press on it), a feeling of heaviness or fatigue in the legs, and itching. The swelling typically improves when you elevate your legs. Over time, though, the condition progresses. Varicose veins become more visible. The skin around your ankles may develop a brownish discoloration from iron deposits leaking out of congested blood vessels. In advanced cases, the skin thickens and hardens, and slow-healing ulcers can form near the inner ankle bone. About 1% to 3% of adults with CVI eventually develop these ulcers.
Heart, Kidney, and Liver Problems
When your heart can’t pump blood efficiently, pressure builds up in your veins, forcing fluid into the tissue of your legs and feet. Heart failure also triggers a cascade of hormonal responses that tell your kidneys to hold onto salt and water, compounding the swelling. The telltale pattern is swelling in both legs that worsens throughout the day, sometimes accompanied by shortness of breath, especially when lying flat.
Kidney disease reduces your body’s ability to filter excess fluid and sodium, leading to fluid overload that often shows up first in the feet and ankles. Liver disease, particularly cirrhosis, lowers your blood’s albumin levels. When albumin drops below a critical threshold (roughly 2 grams per deciliter), there’s not enough protein to pull fluid back into the bloodstream, and swelling becomes widespread.
In all three conditions, the swelling is typically symmetrical, affecting both feet and legs equally. This bilateral pattern is an important clue that distinguishes organ-related swelling from a localized problem like a blood clot or injury.
Swelling During Pregnancy
Some degree of foot and ankle swelling is normal during pregnancy, particularly in the third trimester. Your blood volume increases significantly, and the growing uterus puts pressure on the veins returning blood from your legs.
The concern is preeclampsia, a serious pregnancy complication. The warning signs that separate preeclampsia from normal pregnancy swelling include swelling in the hands, arms, or face (not just the ankles), rapid or unexpected weight gain from fluid retention, blood pressure readings of 140/90 or higher, and protein in the urine. Severe preeclampsia can involve blood pressure of 160/110 or higher along with intense headaches, vision changes, upper abdominal pain, or reduced urine output. These symptoms require immediate medical evaluation.
One Swollen Foot Is Different From Two
The pattern of your swelling matters. Symmetrical swelling in both feet usually points to a systemic cause: too much salt, prolonged sitting, medication side effects, or an organ-related condition like heart failure. Asymmetrical swelling, particularly when only one leg is affected, raises concern for a localized problem.
Deep vein thrombosis, a blood clot in the leg, is the most urgent possibility. Its hallmarks include swelling confined to one leg, calf pain or tenderness, skin that feels warm to the touch, and visible swelling that may extend from below the knee all the way to the groin depending on where the clot sits. If the affected calf measures more than 3 centimeters larger than the other side, that’s a significant clinical finding. A clot that breaks loose and travels to the lungs can be life-threatening, so one-sided leg swelling that appears suddenly warrants same-day medical evaluation.
Other causes of one-sided swelling include an injury, infection, or a blockage in the lymphatic system (lymphedema), which produces a firm, non-pitting type of swelling that doesn’t indent when pressed.
Signs That Need Urgent Attention
Call emergency services if swollen legs are accompanied by chest pain, difficulty breathing, shortness of breath when lying down, fainting, dizziness, or coughing up blood. These can signal a blood clot in the lungs or a serious cardiac event.
Seek same-day medical care if swelling appears suddenly without explanation, follows a physical injury like a fall or accident, or involves only one leg, especially when the skin looks pale or feels cool. Painful, warm, red swelling in one leg also needs prompt evaluation to rule out a clot or infection.
Reducing Swelling at Home
For mild, everyday swelling, elevation is the simplest fix. Propping your feet above heart level for 15 to 20 minutes several times a day lets gravity work in your favor, helping fluid drain back toward your core. If you sit or stand for long stretches at work, take breaks to move around and flex your calf muscles, which act as natural pumps for venous blood.
Cutting back on sodium makes a measurable difference. The American Heart Association recommends staying under 1,500 milligrams per day for the general population. For people managing heart failure, guidelines suggest limiting intake to 2,000 milligrams daily. Since most dietary sodium comes from processed and restaurant foods rather than the salt shaker, reading labels is more effective than simply salting food less.
Compression Stockings
Compression stockings apply graduated pressure to your legs, helping push fluid upward and preventing it from pooling. For occupational swelling caused by prolonged sitting or standing, stockings in the 10 to 15 mmHg range are effective at preventing fluid buildup and are available without a prescription. A slightly higher range of 15 to 20 mmHg offers a bit more support. Research confirms that pressures in the 11 to 21 mmHg range can reduce or completely prevent swelling in people who stand or sit for long periods at work. Knee-high stockings are sufficient for most people with foot and ankle swelling.
For chronic venous insufficiency or more persistent edema, your doctor may recommend medical-grade stockings at 20 to 30 mmHg or higher, which typically require a fitting to ensure proper sizing and pressure distribution.
How Doctors Evaluate Swollen Feet
When you see a doctor for persistent swelling, the exam usually starts with a simple press test. By pushing a thumb into the swollen area for about 20 seconds, they can determine whether the swelling is “pitting” (leaves a dent) or “non-pitting” (bounces right back). Pitting edema is graded on a scale from 1+ to 4+ based on the depth of the indentation: a 1+ pit is 2 to 4 millimeters deep, while a 4+ pit exceeds 8 millimeters. The grade, combined with the location and whether one or both legs are affected, helps narrow down the cause.
From there, basic blood work can check kidney function and albumin levels. An ultrasound of the leg veins can identify clots or valve problems. If a heart condition is suspected, an echocardiogram evaluates how well the heart is pumping. The goal is to find the underlying cause, because treating the root problem is what resolves the swelling long-term.