Ankle edema happens when fluid leaks out of your blood vessels and collects in the tissue around your ankles and feet. The causes range from something as simple as sitting too long or eating a salty meal to serious conditions like heart failure, blood clots, or kidney disease. Whether the swelling affects one ankle or both, and whether it appeared suddenly or gradually, tells you a lot about what’s behind it.
How Fluid Ends Up in Your Ankles
Your body constantly moves fluid between your blood vessels and surrounding tissues. Two forces keep this exchange balanced: the pressure of blood pushing fluid out through vessel walls, and proteins in your blood (mainly one called albumin) pulling fluid back in. When either force shifts, fluid escapes into the tissue and pools wherever gravity pulls it, which usually means your ankles and feet.
Albumin alone accounts for 75 to 80% of the pulling force that keeps fluid inside your blood vessels. Anything that lowers albumin levels or raises blood pressure in your veins will tip the balance toward swelling. Your ankles take the hit because they’re the lowest point in your body when you’re standing or sitting, so leaked fluid naturally settles there.
One Ankle vs. Both: Why It Matters
The single most useful clue is whether the swelling is on one side or both. One-sided swelling usually points to a local problem in that leg, like a blood clot, an injury, or damaged veins. Both ankles swelling together suggests something systemic, meaning a condition affecting your whole body such as heart failure, kidney disease, or a medication side effect.
Chronic venous disease is the most common cause of long-term swelling in both legs. For sudden bilateral swelling, worsening heart failure tops the list. When one leg swells acutely, roughly 40% of the time it turns out to be a muscle strain, tear, or twisting injury rather than a clot, though a blood clot always needs to be ruled out first.
Chronic Venous Insufficiency
Your leg veins have 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, and it’s the single most common reason for persistent ankle swelling.
The swelling from venous insufficiency tends to worsen over the course of the day, especially if you’ve been standing or sitting for hours, and it improves overnight when you’re lying flat. Over time, the skin around your ankles may darken or become discolored. Some people develop itching, flaking, or in advanced cases, open sores near the ankle. A history of blood clots in the leg makes venous insufficiency more likely, since clots can permanently damage the valves.
Heart Failure
When the heart can’t pump blood effectively, pressure builds up in the veins. Blood backs up into the legs, ankles, and feet, forcing fluid out of the vessels and into surrounding tissue. Heart failure typically causes swelling in both legs that develops gradually over weeks or months, though it can worsen suddenly during a flare.
The key distinction with heart failure is that ankle swelling rarely happens alone. You’ll usually notice other symptoms: shortness of breath (especially when lying down or during activity), fatigue, and sometimes swelling in the abdomen. Fluid can also accumulate in the lungs, causing a persistent cough or difficulty breathing. If you have ankle swelling alongside shortness of breath, an irregular heartbeat, or chest pain, that combination needs urgent medical attention.
Kidney and Liver Disease
Your kidneys and liver both play roles in keeping albumin levels normal, and when either organ fails, ankle swelling can follow.
Damaged kidneys can leak large amounts of protein into the urine, a condition called nephrotic syndrome. When protein loss exceeds about 3.5 grams per day, albumin in the blood drops so low that fluid escapes into the tissues. The swelling often shows up first around the eyes in the morning and shifts to the ankles by evening.
The liver manufactures most of the albumin in your blood. In cirrhosis, the liver loses functional tissue and can no longer produce enough albumin to hold fluid inside the vessels. This leads to swelling in both the legs and abdomen. Liver-related edema is often accompanied by visible changes like yellowing of the skin, easy bruising, or a noticeably distended belly from fluid accumulation there.
Blood Pressure Medications
Certain blood pressure drugs are well known for causing ankle swelling. Calcium channel blockers, particularly the subtype called dihydropyridines (amlodipine is the most commonly prescribed), are the main culprits. These medications widen the small arteries but not the veins, creating an imbalance that pushes extra fluid into the tissue around the ankles.
The effect is dose-dependent. At standard doses, ankle swelling occurs in 1 to 15% of people taking these medications. At high doses used long-term, the incidence can exceed 80%. The swelling is not dangerous to the tissue itself, but it can be uncomfortable and persistent. Other medication classes that sometimes cause ankle edema include hormone therapies, certain diabetes drugs, and some anti-inflammatory painkillers.
Pregnancy-Related Swelling
Some degree of ankle swelling is normal in pregnancy, especially in the third trimester. Hormonal changes cause the body to retain extra sodium and water, and the growing uterus can press on the large vein that returns blood from the legs, slowing circulation. This type of swelling is typically symmetrical, affecting both legs equally, and worsens later in the day.
The warning sign is a sudden increase in swelling, particularly if it spreads to the hands or face. That pattern, combined with blood pressure above 140/90, suggests preeclampsia. Preeclampsia no longer requires protein in the urine to be diagnosed; abnormal lab results or symptoms like severe headache and vision changes alongside high blood pressure are enough. Normal pregnancy edema stays in the lower legs and builds gradually. Preeclampsia-related swelling appears rapidly and in unusual locations.
Blood Clots
A deep vein thrombosis (DVT) is a blood clot that forms in one of the deep veins of the leg. It typically causes sudden swelling in one leg only, which is the clearest way to distinguish it from most other causes of ankle edema. Along with the swelling, you may notice pain or tenderness in the calf (often worse when standing or walking), warmth in the swollen area, and skin that looks red or discolored.
DVT is a medical emergency because the clot can break loose and travel to the lungs, blocking blood flow there. Risk factors include recent surgery, prolonged immobility (long flights, bed rest), cancer, and a personal or family history of clotting disorders. Any new, unexplained swelling in a single leg warrants prompt evaluation.
Everyday Causes
Not all ankle swelling signals a medical condition. Prolonged sitting or standing lets gravity pull fluid downward, and without regular muscle movement to pump blood back up through the veins, mild swelling results. This is common after long flights, desk-bound workdays, or any period of inactivity.
High sodium intake plays a direct role too. When you eat excess salt, your kidneys retain extra water to keep the sodium concentration in your blood balanced. That extra fluid increases pressure in your blood vessels and some of it leaks out into the tissues. Heat also contributes: in warm weather, blood vessels near the skin dilate to help release body heat, and the increased flow to the surface can lead to mild fluid leakage around the ankles. These types of swelling are usually mild, temporary, and resolve on their own with movement, elevation, or time.
How Pitting Edema Is Graded
When you press a finger into swollen tissue and it leaves a dent that doesn’t bounce back immediately, that’s called pitting edema. Clinicians grade it on a scale from 1+ to 4+ based on how deep the indentation goes and how far up the leg the swelling reaches. Grade 1 is barely visible with slight pitting. Grade 4 is severe, with deep pitting and swelling that extends above the knee. The grade helps determine how aggressively the underlying cause needs to be investigated and treated.
Non-pitting edema, where pressing doesn’t leave a dent, points to a different set of causes. The most common is lymphedema, which happens when the lymphatic drainage system is blocked or damaged, often after surgery or radiation treatment for cancer. Thyroid disease can also cause a firm, non-pitting type of swelling. If your ankle swelling doesn’t pit when pressed, that distinction is worth mentioning to your provider because it changes the diagnostic direction entirely.