Ankles swell when fluid leaks out of your blood vessels and collects in the tissue around your feet and lower legs. This happens because gravity pulls fluid downward throughout the day, and your body relies on a network of veins, valves, and muscles to push it back up. When any part of that system struggles, or when your body holds onto too much fluid in the first place, your ankles are usually the first place it shows up.
How Fluid Ends Up in Your Ankles
Your capillaries (the tiniest blood vessels) constantly filter fluid in and out of surrounding tissue. Two forces keep this in balance: the pressure of blood pushing fluid out and the pull of proteins in your blood drawing fluid back in. When blood pressure inside the capillaries rises, or when there aren’t enough proteins to pull fluid back, more fluid escapes into the tissue than your lymphatic system can drain. The result is visible swelling, which doctors call edema. It starts around the ankle bones and climbs up the leg the longer fluid accumulates.
Vein Problems Are the Most Common Cause
The veins in your legs contain one-way valves that keep blood moving upward toward your heart. Over time, these valves can weaken or stop closing properly. When that happens, blood flows backward and pools in the lower legs, raising pressure inside the veins and forcing fluid into the surrounding tissue. This condition, chronic venous insufficiency, is extremely common. One large screening study using ultrasound found it in about 9% of men and 7% of women overall, rising to 21% of men and 12% of women over age 50.
You might notice your ankles swell more as the day goes on, especially after standing or sitting for long periods, and the swelling improves overnight when your legs are elevated. Skin changes can develop over time: brownish discoloration near the ankles, thickening or hardening of the skin, and in severe cases, open sores that are slow to heal. About 1% of adults have active or healed venous ulcers.
Heart and Kidney Problems
When the heart can’t pump blood efficiently, pressure backs up in the veins. That elevated pressure pushes more fluid out of the capillaries and into tissue. At the same time, your kidneys sense reduced blood flow and respond by holding onto sodium and water to try to boost blood volume. This creates a cycle: the heart is already overwhelmed, and now it has even more fluid to manage, making the swelling worse.
Up to 60% of people with heart failure also have some degree of kidney dysfunction, which compounds the problem. Kidneys that aren’t filtering well struggle to excrete excess sodium, so fluid retention accelerates. Swelling from heart or kidney disease typically affects both legs equally and may be accompanied by shortness of breath, fatigue, or puffiness in the face and hands.
Too Much Sodium in Your Diet
Your body tightly regulates the concentration of sodium in your blood. When you eat a salty meal, your kidneys retain water to dilute the extra sodium, temporarily expanding your fluid volume. Research on controlled diets ranging from about 2.4 to 4.7 grams of sodium per day showed that higher sodium intake caused a rapid increase in the volume of fluid outside cells. Interestingly, fluid levels returned to baseline after about two weeks even on the highest sodium diet, but blood pressure continued to climb for four weeks. So while your body adapts to some extent, the cardiovascular effects linger.
If your ankles tend to puff up after restaurant meals or processed food, sodium is a likely contributor. The effect is more pronounced if you also have an underlying heart or kidney issue that limits your body’s ability to clear the extra fluid.
Medication Side Effects
Certain blood pressure medications, particularly a class called calcium channel blockers, are well known for causing ankle swelling. These drugs relax the walls of small arteries, which lowers blood pressure but also increases the pressure inside capillaries, pushing fluid into the tissue. The swelling can be significant enough that some people stop taking the medication.
Combining these drugs with another type of blood pressure medication can reduce the edema by about 38% and cuts the rate of people quitting due to swelling by 62%. If you’re on a blood pressure medication and notice new ankle swelling, it’s worth discussing alternatives or combination therapy with whoever prescribes it. Other medications that can cause ankle swelling include certain diabetes drugs, steroids, hormone therapies, and some antidepressants.
Pregnancy and Hormonal Changes
Mild ankle swelling during pregnancy is normal, especially in the third trimester. The growing uterus puts pressure on the veins that return blood from the legs, and hormonal shifts cause the body to retain more fluid. Most of the time this is uncomfortable but harmless.
What changes the picture is speed. A sudden increase in swelling, particularly if it appears in the face or hands along with the ankles, can signal a dangerous blood pressure condition called preeclampsia. Rapid worsening of swelling during pregnancy warrants immediate medical attention.
Prolonged Sitting or Standing
Even in perfectly healthy people, gravity wins if you don’t move. Sitting at a desk all day, a long flight, or standing in one position for hours allows fluid to pool in the lowest part of your body. Your calf muscles normally act as a pump, squeezing veins with each step to push blood back toward the heart. Without that movement, the pump stalls and fluid accumulates. This type of swelling is temporary and resolves with movement or leg elevation.
When Swelling Signals Something Urgent
Swelling in both ankles that develops gradually usually points to one of the causes above: vein problems, fluid retention from diet or medications, or an underlying heart or kidney condition. Swelling in just one leg, especially if it comes on quickly (within 72 hours), tells a different story. A blood clot in a deep vein, known as a DVT, typically causes sudden swelling in one leg along with pain, tenderness, and warmth over the swollen area. The skin may look red or feel hot to the touch. This requires urgent evaluation because the clot can travel to the lungs.
A useful distinction: bilateral swelling that develops over days or weeks and worsens with gravity suggests a systemic cause. Unilateral swelling that appears rapidly with pain and skin color changes suggests a localized problem like a clot or infection.
How to Tell if Your Swelling Is Significant
A simple test you can do at home is pressing a finger firmly into the swollen area for a few seconds, then releasing. If an indentation stays behind, that’s called pitting edema. Clinicians grade it on a scale from 1 to 4 based on how deep the pit is and how long it takes to bounce back:
- Grade 1: A shallow 2mm indent that rebounds immediately
- Grade 2: A 3 to 4mm indent that rebounds within 15 seconds
- Grade 3: A 5 to 6mm indent that takes 15 to 60 seconds to rebound
- Grade 4: An 8mm indent that takes two to three minutes to rebound
Grades 1 and 2 are common with mild fluid retention and often respond to lifestyle changes. Grades 3 and 4 suggest more significant fluid overload and typically warrant medical evaluation to identify the underlying cause.
Practical Ways to Reduce Ankle Swelling
Elevating your legs above heart level for 15 to 30 minutes several times a day lets gravity work in your favor, draining fluid back toward your core. If you sit for long periods, setting a timer to get up and walk for a few minutes every hour activates your calf muscle pump. Flexing and pointing your feet while seated helps too.
Compression stockings apply steady pressure that prevents fluid from settling in the tissue. For mild swelling, stockings rated at 15 to 20 mmHg provide meaningful improvement in both edema and symptoms. For chronic venous disease with persistent swelling, guidelines recommend 20 to 40 mmHg at the ankle. Below-knee styles are sufficient for most people. Higher compression levels (above 30 mmHg) are reserved for more severe cases and can be harder to put on, so starting with a moderate level makes sense unless you’ve been told otherwise.
Reducing sodium intake helps if dietary salt is a contributing factor. Most excess sodium comes from processed and restaurant food rather than the salt shaker, so reading labels and cooking at home gives you the most control. Staying physically active, even with regular walking, strengthens the calf muscle pump and improves venous return over time.