Swollen ankles happen when fluid leaks out of your blood vessels and collects in the surrounding tissue. This is called edema, and it ranges from completely harmless (standing too long on a hot day) to a sign of a serious underlying condition. The key to understanding your swollen ankles starts with a simple question: is one ankle swollen, or both?
How Fluid Ends Up in Your Ankles
Your body constantly moves fluid between your bloodstream and the tissue around it. Two forces keep this process balanced. Pressure inside your blood vessels pushes fluid out, while proteins in your blood (especially one called albumin) pull fluid back in. When something disrupts this balance, fluid escapes faster than your body can reabsorb it, and gravity pulls that extra fluid down to the lowest point: your ankles and feet.
Your lymphatic system acts as a backup drainage network, collecting excess fluid from tissues and returning it to the bloodstream. When lymphatic drainage is impaired, or when inflammation causes blood vessels to become more “leaky,” fluid accumulates even faster. Inflammatory signals from your immune system can actually shut down your lymphatic pumping, making swelling worse during infections or injuries.
One Swollen Ankle vs. Both
Whether the swelling affects one leg or both is the single most useful clue to figuring out the cause. Swelling in just one ankle points toward a local problem: an injury, an infection, a blood clot, or a vein issue in that specific leg. Swelling in both ankles at once suggests something systemic, meaning a condition affecting your whole body like heart, kidney, or liver problems.
There are exceptions. You can have venous disease in both legs at different stages, creating uneven swelling that looks like a one-sided problem. And you can have a systemic condition that causes mild bilateral swelling with a local problem (like a sprain) making one side noticeably worse. But as a general rule, symmetry matters.
Common Everyday Causes
Most ankle swelling isn’t dangerous. Sitting or standing for long stretches, especially during travel, lets gravity do its work. Hot weather causes blood vessels to widen, increasing fluid leakage. Eating a high-sodium meal triggers your kidneys to hold onto more water, expanding the fluid volume in your body. In people who are sensitive to salt, excess sodium accumulates in the skin and draws water into the tissue directly.
Carrying extra weight puts additional pressure on the veins in your legs, making it harder for blood to flow back up to your heart. Even tight shoes or socks with elastic bands can contribute by restricting circulation. In all of these cases, the swelling typically goes down overnight when you’re lying flat and gravity is no longer working against you.
Chronic Venous Insufficiency
The veins in your legs contain one-way valves that keep blood moving upward toward your heart. When those valves weaken or fail, blood pools in the lower legs, raising pressure inside the veins and forcing fluid into the surrounding tissue. This is called chronic venous insufficiency, and it’s one of the most common causes of persistent ankle swelling.
The swelling typically appears around the ankle and lower calf, worsens throughout the day, and improves with rest or leg elevation. Over time, the condition progresses. You may notice varicose veins first, followed by skin discoloration (a brownish pigmentation around the ankles), dry or itchy skin resembling eczema, and in severe cases, skin that becomes hard and leathery. Without management, open sores called venous ulcers can develop near the ankle.
Blood Clots: The Red Flag
A deep vein thrombosis (DVT) is a blood clot that forms in a deep vein, usually in the leg. It causes swelling that’s almost always on one side only, often affecting more of the calf or entire leg rather than just the ankle. Along with swelling, warning signs include pain or cramping that starts in the calf, skin that feels warm to the touch, and a color change (reddish or purplish) in the affected leg.
DVT is a medical emergency because part of the clot can break loose and travel to the lungs. If you have sudden one-sided leg swelling with pain and warmth, especially after surgery, a long flight, or a period of immobility, seek immediate medical attention.
Heart, Kidney, and Liver Problems
When both ankles swell gradually over days or weeks, it can signal that a major organ isn’t working properly.
Heart failure means the heart can’t pump blood efficiently, so pressure builds up in the veins leading back from the legs. The hallmark is ankle swelling that comes with shortness of breath, particularly during physical activity or when lying flat. Some people wake up in the middle of the night gasping for air, a distinctive symptom caused by fluid redistributing when they lie down.
Kidney disease reduces your body’s ability to filter excess sodium and water, leading to fluid buildup throughout the body. It often doesn’t produce obvious symptoms early on, which makes it tricky to catch. The swelling tends to be soft, symmetrical, and may also appear around the eyes in the morning.
Liver cirrhosis lowers the production of albumin, the blood protein that normally pulls fluid back into your vessels. When albumin drops below a critical level, fluid seeps into tissues throughout the body. People with cirrhosis often develop swollen ankles alongside a swollen abdomen (from fluid collecting in the belly), yellowing of the eyes, and visible small blood vessels on the skin.
Thyroid dysfunction, particularly an underactive thyroid, can also cause bilateral ankle swelling, though it’s less common than the three organ systems above.
Medications That Cause Swelling
Several widely prescribed drug classes cause ankle swelling as a side effect. Calcium channel blockers, used for high blood pressure, are among the most common culprits. They work by relaxing the small arteries, which lowers blood pressure but also increases the pressure inside tiny capillaries, pushing fluid out into the tissue. The swelling is dose-dependent: higher doses cause more swelling, and it’s sometimes the reason people have to switch medications.
Other medications that commonly cause fluid retention include:
- Anti-inflammatory painkillers (NSAIDs) like ibuprofen and naproxen, which cause the kidneys to hold onto sodium and water
- Diabetes medications in the thiazolidinedione class, which increase both vascular permeability and kidney fluid retention
- Steroids, which promote sodium retention
- Nerve pain medications like gabapentin and pregabalin
- Some antidepressants and antipsychotics
If your ankle swelling started or worsened shortly after beginning a new medication, that timing is an important clue.
Swollen Ankles During Pregnancy
Some ankle swelling during pregnancy is completely normal, especially in the third trimester. The growing uterus presses on the veins returning blood from the legs, blood volume increases significantly, and hormonal changes make blood vessel walls more permeable.
The concern is preeclampsia, a serious pregnancy complication that develops after 20 weeks. Swelling alone doesn’t diagnose it. The essential feature is new-onset high blood pressure (140/90 or higher on two separate readings) combined with protein in the urine or signs of organ stress. A relative increase in blood pressure or mild swelling during pregnancy isn’t enough by itself, since blood pressure naturally rises somewhat in the third trimester and some fluid retention is expected. But sudden, severe swelling, particularly in the face and hands along with the ankles, paired with headaches, vision changes, or upper abdominal pain, warrants immediate evaluation.
Lymphedema: When Drainage Fails
Lymphedema happens when the lymphatic system can’t adequately drain fluid from a limb. It can be inherited (primary lymphedema) or develop after surgery, radiation therapy, infection, or injury that damages lymph nodes or vessels. It’s particularly common after cancer treatment involving lymph node removal.
What distinguishes lymphedema from venous swelling is where and how it presents. Lymphedema tends to involve the top of the foot and toes, not just the ankle. A classic test is trying to pinch the skin on top of the foot near the base of the second toe. If the skin is too thick and swollen to pinch, that’s a positive Stemmer sign, which strongly suggests lymphedema. In later stages, the skin becomes thickened and rough, nails develop a curved “ski jump” appearance, and the swelling no longer goes away with elevation.
Venous swelling, by contrast, tends to center on the ankle and lower calf, usually improves overnight, and is accompanied by visible vein changes and brownish skin discoloration rather than the skin thickening seen in lymphedema.
What Helps Reduce the Swelling
For everyday, non-dangerous swelling, the basics work well. Elevating your legs above heart level for 15 to 20 minutes several times a day lets gravity help drain the fluid. Moving your feet and ankles regularly, especially during long periods of sitting, activates the calf muscles that pump blood back up through the veins. Reducing sodium intake lowers the amount of fluid your body retains. Compression socks or stockings provide steady external pressure that counteracts fluid leakage, and they’re particularly helpful for chronic venous insufficiency.
For swelling caused by an underlying condition, treating the root problem is what makes the difference. Medication adjustments, management of heart or kidney disease, or specialized lymphatic drainage therapy each address a different mechanism. The swelling itself is the symptom, not the disease, and persistent or worsening ankle swelling that doesn’t respond to elevation and basic measures is worth investigating further.