Swollen feet and ankles happen when fluid leaks out of tiny blood vessels and collects in the surrounding tissue faster than your lymphatic system can drain it away. The medical term is peripheral edema, and the causes range from standing too long on a hot day to serious conditions involving the heart, kidneys, or liver. Understanding what’s behind the swelling often comes down to a few key questions: is it one foot or both, how quickly did it start, and what else is going on in your body?
How Fluid Ends Up in Your Feet
Your body constantly moves water between your bloodstream and the tissue around it. Two opposing forces keep this exchange balanced. Pressure inside your blood vessels pushes fluid outward, while proteins in your blood pull fluid back in. When something disrupts this balance, whether it’s higher pressure in the veins, lower protein levels in the blood, or damage to the vessels themselves, fluid seeps into the tissue and pools in the lowest points: your feet and ankles.
Gravity does the rest. Your legs are the farthest point below your heart, so any excess fluid naturally settles there. The lymphatic system acts as a secondary drainage network, collecting leaked fluid and returning it to the bloodstream. Swelling becomes visible only when the rate of leakage outpaces the lymphatic system’s ability to keep up.
Common Everyday Causes
Most foot and ankle swelling is temporary and tied to lifestyle. Sitting or standing for long stretches, especially during travel, slows blood return from your legs and increases pressure in the veins. Hot weather makes it worse because blood vessels dilate near the skin’s surface to release heat, which lets more fluid escape into surrounding tissue.
Eating too much salt is another frequent trigger. Sodium causes your body to hold onto water, increasing the volume of fluid in your bloodstream and raising pressure in the capillaries. For people already prone to swelling, keeping daily sodium intake between roughly 1,400 and 1,800 milligrams can make a noticeable difference. For context, a single fast-food meal can contain over 2,000 milligrams.
Excess body weight adds mechanical pressure on the veins in your legs and pelvis, making it harder for blood to flow back toward the heart. Even modest weight loss can reduce chronic swelling in some people.
One Leg vs. Both Legs
Whether swelling affects one leg or both is one of the most useful clues to the cause. Swelling in both legs usually points to a systemic issue, something affecting your whole body, like heart failure, kidney disease, liver disease, a medication side effect, or chronic venous insufficiency. Swelling in just one leg is more likely to be a local problem.
A blood clot in a deep vein (deep vein thrombosis) is one of the most serious causes of sudden, one-sided swelling. It typically comes with warmth, redness, or a tight, aching feeling in the calf or thigh. This needs urgent evaluation because the clot can break loose and travel to the lungs.
Lymphedema, where the lymphatic drainage system itself is damaged or blocked, also tends to affect one side. About 75 percent of lymphedema cases are unilateral, with the left leg more commonly involved. It can develop after surgery, radiation, infection, or without any obvious trigger. The swelling tends to feel firmer than fluid-based edema and may not leave an indent when you press on it.
Chronic Venous Insufficiency
Veins in your legs contain one-way valves that keep blood moving upward toward the heart. When those valves weaken or fail, blood flows backward and pools in the lower legs. This is called venous reflux, and it’s one of the most common causes of persistent foot and ankle swelling, especially in people over 50.
The swelling from venous insufficiency is usually worse at the end of the day and improves overnight when your legs are elevated. Over time, the sustained pressure can cause skin changes: darkening, thickening, or a leathery texture around the ankles. Varicose veins are a visible sign that the valves aren’t working properly, though valve failure can also occur in deeper veins you can’t see.
Heart, Kidney, and Liver Conditions
When the heart can’t pump efficiently, blood backs up in the veins. This increases pressure in the leg veins and forces fluid into the surrounding tissue. Heart failure is one of the most common serious causes of bilateral leg swelling, and it often comes with other signs like shortness of breath, fatigue, or waking up at night needing air.
Kidney disease causes swelling differently. Damaged kidneys can’t filter excess fluid and salt from the blood effectively, so fluid volume builds up throughout the body. In some kidney conditions, the filtering units lose protein into the urine, which lowers the protein concentration in the blood. Since those proteins are what pulls fluid back into blood vessels, their loss allows fluid to leak into tissue. Kidney-related swelling often shows up in the legs and around the eyes.
Liver cirrhosis disrupts protein production and raises pressure in the veins draining the abdomen. This combination can cause fluid buildup in the belly and the legs simultaneously.
Medications That Cause Swelling
Several common medications list ankle swelling as a side effect. Blood pressure drugs called calcium channel blockers are among the most frequent culprits. These medications widen blood vessels to lower blood pressure, but they also increase pressure in the small capillaries of the legs, pushing fluid outward. The swelling affects anywhere from 1 to 15 percent of people taking standard doses, but at high doses taken long-term, the rate can exceed 80 percent.
Unlike many side effects that fade as your body adjusts, this type of swelling tends to get worse over time rather than better. One study of over 800 older patients found that the incidence increased gradually the longer treatment continued.
Other medications that can cause foot and ankle swelling include certain diabetes drugs, anti-inflammatory painkillers, steroids, and some hormone therapies. If swelling started shortly after beginning a new medication, that’s worth mentioning to whoever prescribed it.
Pregnancy-Related Swelling
Mild swelling in the feet and ankles is extremely common during pregnancy, especially in the third trimester. The growing uterus compresses pelvic veins, slowing blood return from the legs. Hormonal changes also cause blood vessels to relax and fluid volume to increase.
The concern is when swelling is sudden, severe, or accompanied by other symptoms. Preeclampsia, a potentially dangerous pregnancy complication, involves new-onset high blood pressure (140/90 or higher) plus signs of organ stress, and it can cause generalized, rapid swelling. It typically develops after 20 weeks of pregnancy. Sudden puffiness in the face and hands, persistent headaches, vision changes, or upper abdominal pain alongside worsening leg swelling are warning signs that need immediate medical attention. Severe cases involve blood pressure at or above 160/110.
How Pitting Edema Is Graded
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 pit is and how long it takes to bounce back:
- Grade 1: A 2-millimeter indent that rebounds immediately
- Grade 2: A 3 to 4 millimeter indent that rebounds in under 15 seconds
- Grade 3: A 5 to 6 millimeter indent that takes 15 to 60 seconds to rebound
- Grade 4: An 8-millimeter indent that takes two to three minutes to fill back in
Grade 1 or 2 after a long day on your feet is common and usually not worrisome. Grade 3 or 4, or any grade that persists day after day, suggests something more than just gravity and salt at work.
Managing and Reducing Swelling
For everyday swelling without an underlying medical cause, the basics work well. Elevating your feet above heart level for 20 to 30 minutes several times a day helps gravity work in your favor. Moving your ankles in circles or flexing your calves while sitting keeps the muscle pump active, pushing blood back up through the veins. Regular walking is one of the most effective ways to prevent fluid from pooling.
Compression stockings apply graduated pressure to the legs, tightest at the ankle and gradually loosening toward the knee or thigh. For mild swelling, 20 to 30 mmHg is the most commonly used level and balances effectiveness with comfort. People with more significant venous problems or lymphedema often need 30 to 40 mmHg, which provides firmer support. Stockings at 40 to 50 mmHg or higher are reserved for severe cases and should be fitted with professional guidance.
Reducing sodium intake, staying hydrated (which paradoxically helps your body release excess fluid rather than retain it), and avoiding prolonged sitting or standing all help keep swelling in check. If the swelling is related to an underlying condition like heart failure, kidney disease, or venous insufficiency, treating that condition is what ultimately controls the edema.