Ankle swelling happens when tiny blood vessels called capillaries leak fluid into surrounding tissue. The fluid pools in the lowest parts of your body, which is why ankles and feet are usually the first place you notice it. The causes range from something as simple as sitting too long on a flight to serious conditions involving the heart, kidneys, or veins. Whether the swelling affects one ankle or both is one of the most important clues to what’s behind it.
Why Fluid Collects in the Ankles
Your body constantly moves fluid between your bloodstream and your tissues. Several forces keep this exchange balanced: the pressure inside your blood vessels pushing fluid out, proteins in your blood pulling fluid back in, and your lymphatic system draining whatever’s left over. When any of these systems fails, fluid escapes faster than it can be reabsorbed, and gravity pulls it downward into your ankles and feet.
This is why swelling tends to get worse as the day goes on. Hours of standing or sitting let gravity do its work. Lying down at night redistributes the fluid, which is why many people wake up with thinner ankles that gradually puff up again by evening.
One Swollen Ankle vs. Both
Paying attention to whether one or both ankles are swollen helps narrow the cause significantly. Swelling in just one leg points to a local problem: an injury, an infection, a blood clot, or a blockage in that limb’s drainage system. In a large diagnostic study, about 40% of one-sided leg swelling cases turned out to be a muscle strain, tear, or twisting injury. Another 7% were caused by problems with lymph drainage, and 3% by skin infections like cellulitis.
Swelling in both ankles usually signals something systemic, meaning a condition affecting your whole body. Chronic venous disease is the most common cause of long-standing swelling in both legs. Heart failure, kidney disease, liver disease, and certain medications round out the list.
Deep Vein Thrombosis
A blood clot in one of the deep veins of your leg, known as DVT, is one of the more urgent causes of ankle swelling. The classic signs are swelling in one leg, pain or cramping that often starts in the calf, skin that turns red or purple, and a feeling of warmth over the affected area. Some people with DVT have no noticeable symptoms at all, which makes it especially dangerous.
If you develop sudden, painful swelling in one leg, particularly after a long period of immobility like a hospital stay, a long flight, or recovery from surgery, it warrants prompt medical evaluation. Doctors typically assess your risk level and then use an ultrasound of the leg veins to confirm or rule out a clot. A blood test called d-dimer is sometimes used first as a screening tool. It’s highly sensitive (catching 96% of clots) but not very specific, so a positive result usually leads to an ultrasound for confirmation.
Heart Failure
When your heart can’t pump blood efficiently, fluid backs up in the system. Because the veins in your legs are fighting gravity to return blood to the heart, they’re the first place that backup becomes visible. Swelling from heart failure typically affects both legs and feet, worsens throughout the day, and improves overnight when you’re lying flat.
Other signs that point toward heart failure as the cause include shortness of breath (especially when lying down), waking up gasping at night, unusual fatigue, and abdominal bloating. If your swelling comes with any of these symptoms, the combination is more meaningful than the swelling alone.
Chronic Venous Insufficiency
Your leg veins have one-way valves that keep blood moving upward toward your heart. When those valves weaken or fail, blood pools in your lower legs, a condition called chronic venous insufficiency. It affects roughly 1 in 20 adults and is the single most common cause of long-term ankle swelling.
The swelling from venous insufficiency tends to worsen after prolonged standing and at the end of the day. Over time, the pressure buildup can cause visible changes: varicose veins, skin that turns reddish-brown (especially near the ankles), itching or flaking, and skin that feels leathery or thick. Without treatment, the pressure can eventually burst tiny capillaries in the skin, making the area fragile and prone to open sores near the ankles that heal slowly.
Kidney and Liver Disease
Your kidneys regulate how much fluid stays in your body. When they’re damaged, they can leak protein into the urine, a condition called nephrotic syndrome. Protein in the blood acts like a sponge, pulling fluid back into the bloodstream. When protein levels drop, fluid leaks out into tissues and causes swelling, often in the ankles, feet, and around the eyes.
Liver disease works through a similar mechanism. A damaged liver produces less of the blood proteins that keep fluid in the bloodstream. Advanced liver disease also raises pressure in the veins that drain the lower body, compounding the problem. Both kidney and liver conditions cause bilateral swelling, meaning both ankles are affected equally.
Lymphedema
Your lymphatic system acts as a secondary drainage network, collecting excess fluid from tissues and returning it to your bloodstream. When lymph vessels are damaged or blocked, fluid builds up in the affected area. This is lymphedema, and it looks and feels different from other types of swelling.
The skin over a lymphedema-affected ankle often feels firm rather than squishy. Over time, the tissue thickens and hardens. You may notice a feeling of heaviness or tightness, reduced range of motion, and recurring skin infections in the affected area. Lymphedema commonly develops after cancer treatment that involves removing or irradiating lymph nodes in the pelvis or groin, though it can also be inherited or develop without an obvious cause.
Medications That Cause Swelling
Several common medications cause ankle swelling as a side effect. Blood pressure drugs in the calcium channel blocker family are among the most frequent culprits. Hormone therapies, including estrogen-based birth control and hormone replacement therapy, can also promote fluid retention. Some diabetes medications, anti-inflammatory drugs like ibuprofen, and certain antidepressants round out the list. If your swelling started shortly after beginning a new medication, the timing is worth mentioning to your prescriber.
Pregnancy-Related Swelling
Mild swelling in the feet and ankles during pregnancy is common and usually harmless. Your body retains extra fluid, your blood volume increases, and your growing uterus puts pressure on the veins that return blood from your legs.
What separates normal pregnancy swelling from something more concerning is the pattern. Sudden swelling that comes on quickly, especially in the face or hands, may indicate that blood pressure is climbing too high. This can be a sign of preeclampsia, a serious pregnancy complication. Sudden, painful swelling in just one leg raises the possibility of a blood clot, which pregnant women are at higher risk for. Gradual, symmetrical puffiness in both ankles that improves with rest is usually the benign kind.
How Doctors Find the Cause
Because so many different conditions can cause ankle swelling, the diagnostic process usually starts with blood and urine tests. A standard initial panel checks for heart failure (using a marker called BNP), thyroid problems, liver function, kidney function, and protein loss in the urine. These results, combined with whether the swelling is in one leg or both, how quickly it developed, and what other symptoms are present, guide the next steps.
If heart failure is suspected, an echocardiogram (an ultrasound of the heart) is the usual follow-up. If a blood clot is the concern, compression ultrasound of the leg veins is the standard test. For chronic swelling with skin changes, the clinical appearance alone often points to venous insufficiency or lymphedema without requiring advanced imaging.
Reducing Swelling at Home
Elevating your legs above heart level is the simplest and most effective way to reduce ankle swelling in the short term. Lying on a couch with your feet propped on two or three pillows for 20 to 30 minutes lets gravity drain fluid back toward your core.
Compression socks work by applying graduated pressure that helps push fluid up and out of your lower legs. For mild swelling, over-the-counter socks rated at 15 to 20 mmHg are a reasonable starting point for daily use, travel, or jobs that involve long periods of sitting or standing. Moderate swelling from varicose veins or post-surgical recovery typically calls for 20 to 30 mmHg compression, which is best chosen with a doctor’s input. Severe or chronic conditions like lymphedema or advanced venous insufficiency may require 30 to 40 mmHg prescription-strength stockings.
Reducing salt intake helps because sodium causes your body to hold onto extra water. Regular movement, even short walks or ankle circles while seated, activates the calf muscles that act as pumps to push blood upward through your veins. These strategies manage the symptom, but persistent or worsening swelling needs investigation into the underlying cause.