Foot and ankle swelling happens when fluid leaks out of tiny blood vessels and gets trapped in the surrounding tissue. The causes range from something as simple as standing all day or eating a salty meal to serious conditions involving the heart, kidneys, or veins. Whether your swelling is new or has been creeping in over weeks, understanding the possible triggers helps you figure out what’s worth watching and what needs prompt attention.
How Fluid Ends Up Trapped in Your Feet
Your capillaries, the smallest blood vessels in your body, constantly filter fluid outward into tissue and reabsorb most of it back. This balance depends on four pressures working against each other: the force of blood pushing fluid out, the resistance of surrounding tissue pushing back in, and two opposing protein-based forces that pull fluid toward whichever side has more dissolved protein. When any of these pressures shifts, more fluid escapes than returns, and gravity pulls that excess straight down to your feet and ankles.
Your lymphatic system acts as a backup drain, collecting leftover fluid and returning it to the bloodstream. But this system has limited capacity. When fluid production overwhelms it, or when the lymphatic vessels themselves are damaged, swelling builds up and stays.
Heart Failure and Fluid Overload
Heart failure is one of the most common systemic causes of foot swelling. When the heart can’t pump blood efficiently, pressure builds up in the veins, forcing more fluid out of capillaries and into the tissues. Because blood pools in the lower body due to gravity, the feet and ankles swell first, often worsening throughout the day and improving overnight when you’re lying flat.
Other signs that point toward a heart-related cause include shortness of breath, fatigue, and visible neck vein distension. The swelling in heart failure is almost always bilateral, meaning it affects both feet roughly equally. If you’re over 45 and have unexplained swelling in both legs, a heart evaluation is a reasonable step, since conditions like pulmonary hypertension can quietly drive fluid buildup before other symptoms appear.
Kidney Disease and Protein Loss
Your kidneys play a central role in fluid balance. When they’re damaged, they can leak large amounts of protein into the urine. Normally, proteins in your blood act like sponges, pulling fluid back into your vessels. When protein levels drop below a critical threshold (albumin falling below roughly 2.5 grams per deciliter), that pull weakens and fluid seeps into tissues throughout the body, including the feet, ankles, and often the face and hands.
This pattern, called nephrotic syndrome, involves losing more than 3 to 3.5 grams of protein in the urine over 24 hours. The swelling tends to be soft, widespread, and worse in the morning around the eyes before shifting to the legs as the day goes on. Diabetes, high blood pressure, and certain autoimmune conditions are the most common underlying drivers of this kind of kidney damage.
Venous Insufficiency
The veins in your legs contain one-way valves that push blood upward against gravity. When those valves weaken or fail, blood flows backward and pools in the lower legs, raising pressure inside the veins and pushing fluid into surrounding tissue. This condition, chronic venous insufficiency, is extremely common. National screening data show that varicose veins affect more than 30% of the population, and more than 10% have more advanced venous disease.
The swelling from venous insufficiency usually develops gradually over months or years. It worsens with prolonged standing or sitting and improves with leg elevation. Over time, you may notice skin changes around the ankles: darkening, thickening, or a leathery texture. These are signs the condition has progressed beyond simple swelling. Doctors confirm the diagnosis with an ultrasound that measures the direction of blood flow in the veins. Any significant backward flow lasting more than half a second in the surface veins signals valve failure.
Blood Clots in the Leg
A deep vein thrombosis, or blood clot in one of the deep veins of the leg, causes sudden swelling that typically affects only one foot and calf. This is a key distinguishing feature: swelling in just one leg, especially if it comes on quickly over hours to a few days, raises serious concern for a clot.
The swelling is usually painful, and the affected leg may feel warm or look reddish. Risk factors include recent surgery, prolonged immobility (such as a long flight or bed rest), cancer, and inherited clotting disorders. Because a clot can break loose and travel to the lungs, this cause of foot swelling requires urgent evaluation. If clinical suspicion is low, a simple blood test can effectively rule it out, but a positive result needs follow-up with an ultrasound since false positives on that blood test are common.
Medications That Cause Swelling
Several widely prescribed medications cause fluid retention in the feet and ankles as a side effect. The most well-known culprits are calcium channel blockers, a class of blood pressure medications. These drugs relax blood vessel walls, which lowers blood pressure but also allows more fluid to leak out of capillaries in the lower legs. The swelling is dose-dependent: at standard doses, 1 to 15% of patients experience ankle swelling, but at high doses taken long-term, that figure can exceed 80%.
Combining a calcium channel blocker with certain other blood pressure drugs can cut the risk substantially. In one clinical trial, patients taking amlodipine alone had an edema rate of 18.7%, while those taking it in combination with another blood pressure medication saw that rate drop to 7.6%.
Other medications known to cause foot swelling include:
- NSAIDs like ibuprofen and naproxen, which cause the kidneys to retain sodium and water
- Steroids such as prednisone, particularly at higher doses or with prolonged use
- Diabetes medications in certain classes that promote fluid retention
- Hormonal therapies including estrogen-containing birth control and hormone replacement
If your swelling started shortly after beginning a new medication, that timing is worth mentioning to your prescriber.
Pregnancy and Preeclampsia
Mild foot swelling during pregnancy is normal, particularly in the third trimester, as blood volume increases and the growing uterus compresses veins returning blood from the legs. This type of swelling is usually symmetric, worst at the end of the day, and resolves with rest and elevation.
Swelling that appears suddenly in the hands and face after 20 weeks of pregnancy, however, can signal preeclampsia, a condition defined by high blood pressure (140/90 or above) and protein in the urine (0.3 grams or more over 24 hours). Preeclampsia affects both mother and baby and can escalate quickly. Rapid-onset puffiness in the face, severe headaches, and visual changes alongside foot swelling are warning signs that need immediate evaluation.
Liver Disease
Advanced liver disease disrupts fluid balance in two ways. The liver produces albumin, the main protein that holds fluid inside blood vessels, so a failing liver leads to low albumin levels and widespread swelling. At the same time, scarring in the liver raises pressure in the veins draining the abdomen, which backs up into the legs. Signs that liver disease may be driving your swelling include a distended abdomen from fluid accumulation, yellowing of the skin or eyes, and small red spider-like marks on the upper body.
Lymphedema
When the lymphatic drainage system itself is damaged, fluid accumulates with nowhere to go. This can happen after surgery that removes lymph nodes (common after cancer treatment), after radiation therapy, or from repeated infections that scar the lymphatic channels. In some cases, the lymphatic system is underdeveloped from birth.
Lymphedema swelling feels different from other types. It tends to be firmer, and pressing on it may not leave a visible dent. It usually affects one leg more than the other and worsens progressively over time without treatment. Unlike swelling from heart or kidney problems, it doesn’t respond well to diuretics.
One Foot vs. Both Feet
The pattern of your swelling is one of the most useful clues to its cause. Swelling in just one foot or leg generally points to a local problem: a blood clot, venous insufficiency on that side, lymphatic damage, injury, or infection. Swelling in both feet equally suggests a systemic issue, meaning something affecting your whole body like heart failure, kidney disease, liver disease, or a medication side effect. Generalized swelling that also involves the hands, face, or abdomen further supports a systemic cause.
How Swelling Severity Is Measured
Doctors assess pitting edema by pressing a finger firmly into the swollen area for several seconds and measuring how deep the dent goes and how long it takes to refill. The standard scale runs from grade 1 through grade 4:
- Grade 1: A shallow 2 mm pit that rebounds immediately
- Grade 2: A 3 to 4 mm pit that fills back in under 15 seconds
- Grade 3: A 5 to 6 mm pit that takes 15 to 60 seconds to rebound
- Grade 4: An 8 mm pit that persists for two to three minutes
You can do this test yourself at home. Press your thumb firmly against the inside of your ankle or the top of your foot for about 10 seconds. If you see a lasting dent, you have pitting edema. The deeper the dent and the longer it stays, the more significant the fluid accumulation.
Lifestyle Factors That Contribute
Not all foot swelling stems from a medical condition. Several everyday habits promote fluid retention. High sodium intake is a major one. The World Health Organization recommends staying under 2,000 milligrams of sodium per day (just under a teaspoon of salt), but most people consume well above that. Excess sodium causes your body to hold onto water, and gravity pulls that extra fluid to your feet.
Prolonged sitting or standing keeps blood pooled in the lower legs. Long flights, desk jobs, and occupations that require hours on your feet all contribute. Obesity increases pressure on the veins returning blood from the legs and also promotes inflammation that makes capillaries leakier. Heat causes blood vessels to dilate, which is why many people notice their feet swell more in summer.
Simple countermeasures can make a meaningful difference for mild, lifestyle-related swelling: elevating your feet above heart level for 20 to 30 minutes, wearing compression socks, taking walking breaks during long periods of sitting, reducing processed food intake to lower sodium, and staying physically active to support the muscle contractions that pump blood back up from the legs.