Ankle swelling happens when fluid accumulates in the tissues around your ankle joint. The causes range from something as simple as sitting too long to serious conditions like heart failure or blood clots. One of the most useful clues is whether the swelling affects one ankle or both, because that distinction points toward very different underlying problems.
One Ankle vs. Both: Why It Matters
Swelling in a single ankle typically points to a local problem: an injury, infection, or blocked blood flow in that leg. When both ankles swell at the same time, it usually signals something systemic, meaning a condition affecting your whole body like heart disease, kidney problems, or a medication side effect.
When one leg swells suddenly, the most important thing to rule out is a blood clot (deep vein thrombosis). After that’s been excluded, the most common explanations break down roughly like this: about 40% of cases turn out to be a muscle strain, tear, or twisting injury. Around 7% are from chronic vein problems in that leg, and smaller percentages come from infections, cysts behind the knee, or joint issues. In about a quarter of cases, no specific cause is identified.
Sudden swelling in both ankles is most commonly caused by worsening heart failure. Chronic swelling in both ankles is most often from venous disease, though heart failure, sleep apnea, kidney disease, and liver disease can all contribute.
Venous Insufficiency
The single most common cause of chronic ankle swelling is a problem with the veins in your legs. 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 your lower legs. This is called chronic venous insufficiency.
The pooling blood raises pressure inside your leg veins so much that your smallest blood vessels, the capillaries, can eventually burst. Fluid leaks out into the surrounding tissue, and over time, scar tissue can develop in the lower leg that traps even more fluid. You’ll often notice the swelling worsens throughout the day and improves overnight when your legs are level with your heart. Skin color changes, a brownish discoloration around the ankles, and eventually ulcers can develop if it goes untreated.
Heart, Kidney, and Liver Problems
When your heart can’t pump blood efficiently, the flow returning from your legs slows down. Blood backs up in the veins, and fluid leaks out into the tissues. This is why swollen ankles are one of the hallmark signs of heart failure. The swelling is typically worse in the evening, and you may also notice shortness of breath, fatigue, or difficulty lying flat at night.
Your kidneys regulate how much fluid and salt stay in your body. When they aren’t filtering properly, excess sodium and water build up in your bloodstream and eventually settle into your lower extremities. Liver disease works through a different mechanism: a damaged liver produces less of a protein called albumin, which normally keeps fluid inside your blood vessels. Without enough of it, fluid seeps out into surrounding tissues.
All three of these organ-related causes tend to produce swelling in both ankles symmetrically, and the swelling typically leaves an indent when you press on it (called pitting edema).
How to Check the Severity of Swelling
Doctors assess ankle swelling by pressing a finger into the swollen area for a few seconds and measuring how deep the dent is and how quickly it bounces back. This is graded on a four-point scale:
- Grade 1: A shallow 2 mm dent that rebounds immediately
- Grade 2: A 3 to 4 mm dent that fills back in within 15 seconds
- Grade 3: A 5 to 6 mm dent that takes up to 60 seconds to rebound
- Grade 4: An 8 mm dent that persists for two to three minutes
You can do this yourself at home. If pressing your thumb firmly into the skin above your ankle bone leaves a visible dent that lingers for more than a few seconds, that suggests more than mild fluid retention.
Medications That Cause Ankle Swelling
Certain blood pressure medications, particularly a class called calcium channel blockers, are well-known for causing ankle swelling. Research published in the American Heart Association’s journal Hypertension found that the effect isn’t just an occasional side effect. It’s a consistent, dose-dependent response: higher doses produce more fluid accumulation in the legs. The study measured actual increases in leg weight at different doses, confirming that this happens to some degree in most people taking these drugs, not just those who develop visible swelling.
Other medications that commonly cause ankle swelling include hormone therapies (like estrogen or testosterone), some diabetes medications, anti-inflammatory drugs like ibuprofen and naproxen, and certain antidepressants. If your ankle swelling started or worsened shortly after beginning a new medication, that connection is worth discussing with whoever prescribed it.
Lifestyle and Temporary Causes
Not all ankle swelling points to a medical condition. Gravity alone can cause fluid to pool in your feet and ankles when you sit or stand in one position for hours. Long flights, desk jobs, and road trips are common culprits. A high-sodium diet accelerates the effect because salt causes your body to hold onto extra water. Processed meats, canned soups, chips, cheese, and fast food are among the biggest sodium sources in most diets.
Alcohol also contributes to fluid retention. Heat plays a role too: warm weather causes blood vessels to dilate, which allows more fluid to move into surrounding tissues. These types of swelling are usually mild, affect both ankles equally, and resolve once you move around, elevate your legs, or reduce your salt intake.
Ankle Swelling During Pregnancy
Some degree of ankle swelling is normal in the later months of pregnancy. Your body retains more fluid, your blood volume increases significantly, and the weight of the uterus compresses veins that return blood from your legs. Mild, symmetrical swelling that comes and goes is expected.
What’s not normal is sudden, severe swelling, especially if it’s accompanied by headaches, vision changes, or upper abdominal pain. These can be signs of preeclampsia, a dangerous pregnancy complication involving high blood pressure. Blood pressure at or above 140/90 mm Hg during pregnancy raises concern. Preeclampsia can now be diagnosed even without protein in the urine if other abnormal findings are present, so sudden worsening of ankle swelling in pregnancy warrants prompt evaluation.
Blood Clots: The Serious Red Flag
A deep vein thrombosis (DVT) forms when a blood clot develops 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.
The reason DVT is treated as urgent is that the clot can break loose and travel to your lungs, causing a pulmonary embolism. Warning signs of that include sudden shortness of breath, chest pain that worsens when you breathe deeply or cough, dizziness or fainting, a rapid pulse, or coughing up blood. A pulmonary embolism is a medical emergency.
Risk factors for DVT include recent surgery, prolonged immobility (like bed rest or a long flight), cancer, pregnancy, obesity, and a personal or family history of blood clots. If you have new, unexplained swelling in one leg with pain or skin color changes, that combination warrants same-day medical evaluation.
Infections and Injuries
Sprains, fractures, and torn tendons all cause localized ankle swelling as part of the body’s inflammatory healing response. This type of swelling is usually obvious because you’ll remember the injury, and it’s accompanied by pain, bruising, or difficulty bearing weight.
Cellulitis, a bacterial skin infection, can also cause one ankle to swell. It typically produces redness, warmth, and tenderness in the affected area, sometimes with fever. Cellulitis requires antibiotic treatment because the infection can spread. Gout is another possibility, especially if the swelling comes on suddenly with intense pain and redness, often starting in the big toe but sometimes affecting the ankle joint.