Swollen ankles happen when fluid leaks out of your blood vessels and collects in the tissues of your lower legs. Gravity pulls that fluid downward throughout the day, which is why the ankles and feet are usually the first place you notice it. The causes range from something as simple as sitting too long to serious conditions involving your heart, kidneys, or veins.
How Fluid Ends Up in Your Ankles
Your body constantly moves fluid between your bloodstream and the surrounding tissues. Four things keep this exchange balanced: the pressure inside your blood vessels pushing fluid out, proteins in your blood pulling fluid back in, the integrity of your vessel walls, and your lymphatic system draining any excess. When any of these forces shifts, fluid starts accumulating in your tissues instead of staying where it belongs.
The veins on the arterial side of your capillaries push fluid outward at higher pressure, while the venous side reabsorbs it. The venous end has poor ability to regulate pressure changes, so anything that raises venous pressure (standing all day, a weakened heart, a blood clot) translates almost directly into more fluid being forced into your tissues. Your ankles sit at the lowest point, so that’s where fluid pools first.
Chronic Venous Insufficiency
This is one of the most common causes of swollen ankles, affecting an estimated 10% to 35% of adults in the United States. The veins in your legs contain one-way valves that keep blood moving upward toward your heart. When those valves weaken or fail, blood flows backward and pools in your lower legs, raising the pressure inside those veins. That sustained high pressure forces fluid out into the surrounding tissue.
Venous insufficiency tends to develop gradually. You might first notice your ankles swelling after long days on your feet, then find the swelling takes longer to go down overnight. Over time, the skin on your lower legs can darken, become itchy, or feel tight. In advanced cases, the persistent pressure damages tiny blood vessels and can eventually lead to open sores near the ankles. Women are affected more often than men, and risk rises significantly after age 65.
Heart Failure
When the heart can’t pump blood efficiently, pressure builds in the veins leading back to it. That backup raises the pressure in your leg veins and pushes fluid into your tissues. At the same time, your kidneys sense that less blood is flowing through them and respond by holding onto sodium and water to try to maintain blood volume. This creates a cycle: more fluid in the system, more pressure in the veins, more swelling.
Heart failure typically causes swelling in both ankles equally. The swelling tends to worsen over the course of the day and improve after a night of sleep with your legs elevated. If fluid also backs up into the lungs, you may notice shortness of breath, especially when lying flat. These symptoms together, bilateral ankle swelling plus breathlessness, are a strong signal that the heart is involved.
Kidney Disease
Your kidneys filter excess sodium and water from your blood. When they’re damaged, they can’t remove enough of either, and the extra fluid builds up in your blood vessels and leaks into tissues. Kidney disease can also cause your body to lose large amounts of protein through your urine, a condition called nephrotic syndrome. Those proteins normally act like sponges in your bloodstream, pulling fluid back in. Without enough of them, fluid escapes more easily into surrounding tissue, causing swelling in the legs, face, and around the eyes.
Medications That Cause Swelling
Certain blood pressure medications are a surprisingly common culprit. Calcium channel blockers, particularly the type called dihydropyridines (amlodipine is the most widely prescribed), widen your arteries to lower blood pressure but don’t have the same effect on veins. This mismatch raises the pressure inside your capillaries and pushes fluid out. A large multicenter study found that nearly 39% of patients on these drugs developed peripheral edema. The risk is dose-dependent: patients taking a higher dose developed swelling at a rate of about 43%, compared to 33% on a lower dose.
Other medications known to cause ankle swelling include certain diabetes drugs, anti-inflammatory painkillers like ibuprofen (which cause the kidneys to retain sodium), hormone therapies including estrogen, and some antidepressants. If your ankle swelling started shortly after beginning a new medication, that timing is worth noting.
Pregnancy-Related Swelling
Some degree of ankle swelling is normal during pregnancy, especially in the third trimester. The growing uterus puts pressure on the veins that return blood from your legs, and your body retains more fluid overall to support the baby. This type of swelling tends to come on gradually and affects both legs.
What’s not normal is sudden swelling, particularly in the face and hands. This can be a sign of preeclampsia, a serious pregnancy complication defined by high blood pressure and signs of organ damage. Other warning signs include severe headaches, vision changes like blurriness or light sensitivity, pain under the ribs on the right side, and nausea. Preeclampsia can develop after 20 weeks of pregnancy and requires immediate medical attention.
Blood Clots in the Leg
Deep vein thrombosis, a blood clot in one of the deep veins of the leg, is one of the more dangerous causes of ankle swelling. The key distinction is that it almost always affects one leg. Along with swelling, you may notice pain or cramping that starts in the calf, warmth in the affected area, and skin that looks red or purple. Some blood clots cause no noticeable symptoms at all, which makes them particularly risky since a clot can break free and travel to the lungs.
Risk factors include recent surgery, long flights or car rides, prolonged bed rest, cancer, and use of hormonal birth control. If one ankle swells suddenly and the other doesn’t, especially with calf pain or warmth, that warrants urgent evaluation.
Everyday Causes
Not all ankle swelling points to a medical condition. Sitting or standing in one position for hours allows gravity to pull fluid into your lower legs. Long flights are a classic example. Hot weather dilates your blood vessels and makes them leakier. Eating a high-sodium meal causes your kidneys to retain water temporarily, and that extra fluid can settle in your ankles. Being overweight puts additional pressure on the veins in your legs and pelvis, making it harder for blood to return to your heart efficiently.
Reducing sodium intake is one of the most practical steps for managing fluid retention. Guidelines for people with heart-related edema suggest keeping sodium between 1,500 and 3,000 milligrams per day, but even people without heart disease often benefit from staying under 2,300 milligrams. For context, a single restaurant meal can easily contain over 2,000 milligrams.
How Swelling Is Assessed
Doctors evaluate ankle swelling with a simple physical test: pressing a finger into the swollen area for several seconds and watching what happens. If the pressure leaves a visible dent that takes time to bounce back, it’s called pitting edema, and it’s graded on a four-point scale:
- Grade 1: A shallow 2 mm pit that rebounds immediately
- Grade 2: A 3 to 4 mm pit that rebounds 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 takes two to three minutes to fill back in
Grades 1 and 2 are common with mild fluid retention from sitting too long or eating a salty meal. Grades 3 and 4 typically point to a more significant underlying cause, such as heart failure, kidney disease, or severe venous insufficiency. The depth and rebound time help guide how aggressively the cause needs to be investigated.
One Ankle vs. Both
Whether one or both ankles are swollen is one of the most useful clues to the cause. Swelling in both ankles that develops gradually and worsens over time points toward a systemic issue: heart failure, kidney disease, medication side effects, or venous insufficiency. Sudden swelling in just one leg raises concern for a blood clot or a localized injury like a sprain or infection. An infection will usually also cause redness, warmth, and tenderness concentrated in one area. If both ankles are swollen but one is significantly worse, venous insufficiency in that leg or a partial clot is possible.