Swollen feet and ankles happen when fluid leaks out of small blood vessels and collects in the surrounding tissue faster than your lymphatic system can drain it away. The causes range from something as simple as standing too long to serious conditions like heart failure or blood clots. Understanding the pattern of your swelling, whether it affects one leg or both, and what other symptoms come with it can help you figure out what’s behind it.
How Fluid Builds Up in Your Lower Body
Your body constantly moves fluid between your bloodstream and the tissue around it. A balance of pressure inside your blood vessels, pressure outside them, and protein levels in your blood keeps everything in check. When something disrupts that balance, fluid seeps into the spaces between cells and pools in the lowest point gravity can pull it: your feet and ankles.
If the excess fluid accumulates faster than your lymphatic system (a network of vessels that acts like a drainage system) can return it to your bloodstream, visible swelling appears. This is why swelling tends to worsen throughout the day and improve overnight when you’re lying flat.
Everyday Causes That Aren’t Dangerous
Prolonged sitting or standing is one of the most common triggers. When your leg muscles aren’t contracting, they can’t help push blood back up toward your heart, so fluid pools in your lower legs. Long flights, desk jobs, and car rides are classic culprits. Hot weather compounds the problem because heat causes blood vessels to widen, making it easier for fluid to leak into surrounding tissue.
Eating a lot of salty food can also cause temporary swelling. Sodium makes your body hold onto water, and that extra fluid has to go somewhere. Tight shoes, minor ankle injuries, and simply being on your feet all day round out the list of harmless, short-lived causes. This type of swelling is usually symmetrical (both feet), painless, and resolves on its own with rest and elevation.
Chronic Venous Insufficiency
Your veins have one-way valves that keep blood flowing upward against gravity. When those valves weaken or fail, blood flows backward and pools in your lower legs, a condition called chronic venous insufficiency (CVI). It’s surprisingly common. A large Scottish study using ultrasound screening found CVI in about 9% of men and 7% of women overall, rising sharply with age to 21% of men and 12% of women over 50.
CVI typically causes swelling that worsens as the day goes on, along with aching, heaviness, and visible varicose veins. Over time, the skin around your ankles may darken or become leathery. The swelling affects both legs in most cases, though one side can be worse than the other. Doctors confirm CVI with a vascular ultrasound that measures how long blood flows backward through the valves. A reflux time longer than half a second in superficial veins signals a problem.
Heart, Kidney, and Liver Disease
When your heart can’t pump blood efficiently, the flow returning from your legs slows down. Blood backs up in the veins, pressure builds, and fluid leaks into the tissue. Swelling in the ankles, lower legs, and abdomen is one of the hallmark signs of heart failure. The swelling is typically symmetrical and may come with shortness of breath, fatigue, and unexplained weight gain from fluid retention.
Kidney disease causes swelling through a different path. Damaged kidneys can’t filter sodium and water properly, so excess fluid stays in your body. They may also let protein leak into your urine, which lowers the protein concentration in your blood. Since blood proteins help pull fluid back into your vessels, losing them means more fluid escapes into your tissues.
Liver disease, particularly cirrhosis, reduces the liver’s ability to produce those same blood proteins. The result is similar: fluid shifts out of the bloodstream and into the tissue. Liver-related swelling often shows up in the abdomen first but can extend to the legs and feet.
Medications That Cause Swelling
Several common medications list swollen ankles as a side effect, but calcium channel blockers (often prescribed for high blood pressure) are the biggest offenders. Between 1% and 15% of people taking standard doses develop ankle swelling, and at higher doses taken long term, that number can exceed 80%. Unlike other causes of edema, this type of swelling isn’t from your body retaining extra fluid. It’s caused by the medication relaxing blood vessel walls so much that fluid redistributes from inside the vessels into surrounding tissue.
Other medications linked to lower-leg swelling include certain diabetes drugs, steroids, hormone therapies like estrogen, and some antidepressants. If your swelling started shortly after beginning a new medication, that connection is worth exploring with your prescriber. Stopping or switching the drug often resolves the problem.
Swelling During Pregnancy
Some degree of foot and ankle swelling is normal in pregnancy, especially in the third trimester. Your blood volume increases significantly, your growing uterus puts pressure on the veins returning blood from your legs, and hormonal shifts cause your blood vessels to relax.
The concern is preeclampsia, a serious pregnancy complication. The key differences: preeclampsia causes sudden swelling in the hands, arms, or face (not just the ankles), along with high blood pressure of 140/90 mmHg or above. Severe preeclampsia involves blood pressure of 160/110 or higher. Normal pregnancy swelling stays in the ankles and feet, develops gradually, and isn’t accompanied by headaches, vision changes, or upper abdominal pain. Rapid swelling that appears in your hands or face, or a sudden jump in weight from fluid retention, warrants prompt medical attention.
Blood Clots: The One-Sided Warning Sign
Deep vein thrombosis (DVT) is a blood clot that forms in a deep vein, usually in the leg. It’s one of the more urgent causes of swelling because the clot can break free and travel to the lungs, causing a pulmonary embolism. The distinguishing feature of DVT is that it almost always affects just one leg. The swelling may come on suddenly and is typically accompanied by pain or tenderness (especially when walking or standing), warmth in the swollen area, and skin that looks red or discolored.
A pulmonary embolism is a medical emergency. Symptoms include sharp chest pain that worsens with deep breaths, sudden shortness of breath even at rest, a fast heartbeat, coughing up blood, and pale or bluish skin. If you have leg swelling on one side combined with any of these symptoms, call 911.
How Doctors Assess Swelling Severity
When you visit a doctor for swollen feet or ankles, they’ll likely press a finger into the swollen area for several seconds. If the pressure leaves a visible dent, it’s called pitting edema, and it’s graded on a 1 to 4 scale based on how deep the pit is and how quickly it bounces back:
- Grade 1: A shallow 2 mm dent that rebounds immediately
- Grade 2: A 3 to 4 mm dent that rebounds in under 15 seconds
- Grade 3: A 5 to 6 mm dent that takes 15 to 60 seconds to rebound
- Grade 4: An 8 mm dent that takes two to three minutes to fill back in
Higher grades generally point toward more significant underlying causes, though the grade alone doesn’t tell your doctor the reason. Blood tests, ultrasound, and urine tests may follow depending on what the physical exam suggests.
Managing Swelling at Home
For mild, non-dangerous swelling, a few strategies make a real difference. Elevating your legs above heart level for 20 to 30 minutes several times a day helps gravity move fluid back toward your core. Regular movement, even short walks or calf raises, activates the muscle pump in your lower legs that pushes blood upward.
Compression stockings apply graduated pressure to your legs, with the tightest squeeze at the ankle. Low-compression stockings (under 20 mmHg of pressure) are available without a prescription and work well for mild swelling from prolonged sitting or standing. Stockings rated 20 mmHg or higher require a prescription and are typically used for chronic venous insufficiency or more persistent edema.
Reducing sodium intake helps if fluid retention is a factor. The general recommendation for people prone to fluid buildup is to stay under 2,000 to 3,000 mg of sodium per day. For people with moderate to severe heart failure, the target drops below 2,000 mg, roughly the amount in a single fast-food meal. Reading labels matters here, since processed and restaurant foods account for the majority of sodium in most diets.
Patterns That Point to the Cause
The details of your swelling carry diagnostic clues. Swelling in both legs that develops gradually and worsens by evening suggests venous insufficiency, prolonged standing, or a systemic cause like heart or kidney trouble. Swelling that appeared after starting a new blood pressure medication points to a drug side effect. One-sided swelling with pain and warmth raises concern for a blood clot. Swelling that doesn’t pit when you press on it can indicate lymphatic problems or thyroid disease rather than fluid retention.
Pay attention to what makes it better or worse. Swelling that resolves completely overnight and returns by afternoon is more likely positional or venous. Swelling that persists around the clock, or gradually worsens over weeks, suggests something systemic that needs evaluation.