Ankle swelling happens when fluid builds up in the tissues around your ankle joint, and the causes range from something as simple as sitting too long to serious conditions involving your heart, kidneys, or blood vessels. Whether the swelling affects one ankle or both is one of the most important clues to what’s behind it.
Why One Ankle vs. Both Matters
Swelling in a single ankle points to a local problem: an injury, a blood clot, an infection, or a blockage in the lymphatic system on that side. When both ankles swell at the same time, the cause is more likely something systemic, meaning a condition affecting your whole body, like heart failure, kidney disease, or a medication side effect.
When researchers have looked at people who show up with swelling in just one leg (after ruling out a blood clot), the breakdown is roughly 40% muscle strain or injury, 7% lymphatic obstruction, 7% vein problems, and 5% a fluid-filled cyst behind the knee. In about a quarter of cases, no clear cause is found. Chronic swelling in both legs, on the other hand, is most commonly tied to problems with the veins, followed by heart failure, sleep apnea-related lung changes, and less often kidney or liver disease.
Vein Problems Are the Most Common Cause
Your leg veins contain one-way valves that push blood upward toward your heart against gravity. When those valves weaken or get damaged, blood flows backward and pools in the lower legs. This condition, called chronic venous insufficiency, is the single most common reason for persistent ankle swelling.
Valve damage can happen in a few ways. Some people are born with veins that have poorly formed or even missing valves. Others develop valve damage over time from standing or sitting for long hours, obesity, pregnancy, or simply aging. A previous blood clot in a deep leg vein can also scar the valves permanently. Once blood begins pooling, pressure rises inside the veins and forces fluid out into the surrounding tissue. Over time you may also notice skin discoloration, a brownish tint around the ankles, or in severe cases, open sores.
Blood Clots: The Urgent Cause
A deep vein thrombosis (DVT) is a blood clot that forms in one of the large veins deep inside your leg. It typically causes swelling in just one leg, along with pain or cramping that often starts in the calf, warmth in the affected area, and skin that looks red or purple. DVT is a medical emergency because the clot can break free and travel to the lungs, cutting off blood flow there.
Risk factors include recent surgery, long flights or car rides, bed rest, cancer, pregnancy, and use of hormonal birth control. If you develop sudden swelling in one ankle with pain, warmth, or skin color changes, that combination warrants urgent medical evaluation.
Heart Failure and Fluid Backup
When the heart can’t pump blood efficiently, pressure builds in the veins that return blood from the legs. That increased pressure pushes fluid out of the blood vessels and into the tissue around your ankles and feet. Swelling from heart failure is almost always in both legs and tends to worsen over the course of the day, especially if you’ve been on your feet. You may also notice shortness of breath, fatigue, or waking up at night gasping for air.
The swelling typically leaves an indentation when you press on it with your finger. Doctors grade this “pitting” 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 instantly. A grade 4 pit is about 8 millimeters deep and takes two to three minutes to fill back in. Higher grades generally signal more significant fluid overload.
Kidney and Liver Disease
Your kidneys and liver both play a role in keeping fluid balanced in your body, and when either organ falters, the ankles are often where excess fluid shows up first.
The key player is a protein called albumin, which makes up about 75 to 80% of the force that keeps fluid inside your blood vessels. Healthy kidneys filter waste but hold onto albumin. In kidney disease, particularly a condition called nephrotic syndrome, the kidneys leak albumin into the urine. With less albumin in the blood, fluid seeps out of blood vessels and settles in the lowest points of the body: your ankles and feet.
Liver disease works through a similar mechanism but from the production side. The liver manufactures albumin, and when liver cells are damaged, as in cirrhosis, production drops. Even though the body sometimes tries to compensate by ramping up whatever liver function remains, the albumin concentration in the blood still falls because it gets diluted. The result is the same: fluid leaks into tissues, causing swelling in the ankles, legs, and often the abdomen.
Medications That Cause Ankle Swelling
Certain blood pressure medications are well-known culprits. Calcium channel blockers, a class of drugs commonly prescribed for high blood pressure, cause ankle swelling in 1 to 15% of people at standard doses. At higher doses taken long-term, that number can exceed 80%. These drugs work by relaxing blood vessels, but they relax the arteries more than the veins. The mismatch increases pressure in the small blood vessels of the legs, pushing fluid into surrounding tissue.
Adding a second type of blood pressure medication can help. In one trial, people taking a calcium channel blocker alone had an 18.7% rate of ankle swelling, while those taking it in combination with an ACE inhibitor saw just 7.6%. Other medications that can trigger ankle swelling include hormone therapies like estrogen, certain diabetes drugs, anti-inflammatory painkillers, and some antidepressants.
Lymphedema
Your lymphatic system is a network of vessels that drains excess fluid from tissues and returns it to the bloodstream. When these vessels are blocked or damaged, fluid accumulates, typically in one limb. Lymphedema in the legs often develops after surgery or radiation therapy that removes or damages lymph nodes in the groin or pelvis, which is why it’s common after certain cancer treatments.
Lymphedema feels different from vein-related swelling. The skin may feel firm or spongy rather than soft, and pressing on it may not leave a dent the way other types of swelling do. Over time, the skin can thicken and harden. Unlike venous swelling, which tends to concentrate around the ankle and lower calf, lymphedema often affects the entire limb more evenly, sometimes extending up the thigh.
Pregnancy
Some ankle swelling during pregnancy is normal, especially in the third trimester. The growing uterus puts pressure on the large veins returning blood from the legs, and hormonal changes cause the body to retain more fluid. Most pregnant women notice their ankles are puffiest at the end of the day or in warm weather.
What’s not normal is sudden, severe swelling, especially if it comes with a headache, vision changes, or upper abdominal pain. This combination can signal preeclampsia, a serious pregnancy complication involving high blood pressure and organ stress. Gradual, mild swelling in both ankles that improves overnight is typical pregnancy edema. Rapid onset or swelling that doesn’t go away warrants a call to your provider.
Everyday Factors
Not all ankle swelling signals a medical condition. Gravity alone can do it. Sitting in one position for hours, whether at a desk or on a long flight, lets fluid pool in your lower legs. Standing all day has the same effect. Hot weather dilates blood vessels near the skin’s surface and increases fluid leakage into tissues. Eating a high-sodium meal can cause your body to retain extra water, and that fluid often settles in the ankles.
For people who deal with chronic mild swelling, sodium intake makes a real difference. General dietary guidelines recommend staying under 2,300 milligrams of sodium a day, but for people with persistent edema, a tighter range of 1,375 to 1,800 milligrams daily is often recommended. That’s roughly the equivalent of cutting out most processed foods and not adding salt at the table. Elevating your legs above heart level for 15 to 20 minutes several times a day, wearing compression socks, and staying physically active all help move fluid back into circulation.