Swollen feet and ankles result from fluid collecting in the tissues of your lower legs, a condition called edema. The causes range from something as simple as sitting too long or eating a salty meal to serious conditions like heart failure, kidney disease, or blood clots. Whether the swelling affects one leg or both, came on suddenly or built up over weeks, and whether it’s painful or painless all point toward different causes.
One Leg vs. Both: Why It Matters
One of the most useful clues is whether the swelling is in one leg or both. Swelling in a single leg usually points to a local problem: an injury, infection, blood clot, or damaged veins in that leg. Swelling in both legs at the same time is more likely caused by something systemic, meaning a condition affecting your whole body like heart failure, kidney problems, or a medication side effect.
This isn’t a hard rule. Chronic venous disease is actually the most common cause of long-term swelling in both legs. But sudden swelling in one leg that’s also warm, red, or painful deserves urgent attention because it may signal a deep vein thrombosis (DVT), a blood clot in a deep leg vein.
Venous Insufficiency
The single most common cause of chronic foot and ankle swelling is a problem with the veins in your legs. Your leg veins contain one-way valves that push blood upward toward your heart against gravity. When those valves weaken or become damaged, blood flows backward and pools in your lower legs. The increased pressure forces fluid out of the blood vessels and into the surrounding tissue, causing visible swelling.
This condition, called chronic venous insufficiency, develops gradually. You might notice your ankles are puffy by the end of the day but look normal in the morning. Over time, the swelling can become persistent, and you may develop skin discoloration, varicose veins, or even open sores on your lower legs. Carrying extra weight puts additional pressure on these valves and accelerates the damage. A prior blood clot (DVT) can also permanently damage the valves in the affected vein, leading to long-term swelling in that leg.
Heart, Kidney, and Liver Disease
When swelling appears in both legs and gets worse over time, it can signal that a major organ isn’t working properly.
In congestive heart failure, the heart can’t pump blood efficiently. Blood backs up in the veins, and the pressure pushes fluid into the tissues of your legs, ankles, and feet. This type of swelling often comes with other symptoms: shortness of breath, fatigue, and difficulty lying flat to sleep.
Kidney disease causes swelling through a different mechanism. Your kidneys normally filter excess fluid and salt from your blood. When they’re damaged, fluid and salts build up in the body. A specific type of kidney damage called nephrotic syndrome causes protein to leak out of the blood, which pulls even more fluid into the tissues.
Liver damage from cirrhosis can also cause fluid buildup, typically in the abdomen first and then in the legs. This happens because a scarred liver can’t produce enough of the proteins that help keep fluid inside blood vessels.
Salt, Sitting, and Other Everyday Causes
Not every case of swollen ankles points to a disease. Several everyday factors cause temporary fluid retention in your lower legs.
- High sodium intake. Eating a lot of salty food causes your body to hold onto extra water to maintain the right balance of electrolytes. Your skin actually acts as a reservoir for sodium, and excess salt creates pressure gradients that pull fluid into your tissues.
- Prolonged sitting or standing. Gravity constantly pulls fluid downward. When you sit at a desk for hours or stand in one position all day, your calf muscles aren’t contracting enough to help push blood back up. Fluid accumulates in your feet and ankles.
- Heat. Warm temperatures cause blood vessels to widen, which allows more fluid to seep into surrounding tissues. This is why your shoes may feel tighter on hot days.
- Medications. Several common drugs can cause ankle swelling as a side effect, particularly certain blood pressure medications (calcium channel blockers), hormonal therapies, and some anti-inflammatory drugs.
These causes typically produce mild swelling that goes down overnight or after you elevate your legs. If it doesn’t resolve, something else may be going on.
Injuries and Inflammation
A sprained ankle is one of the most obvious causes of sudden swelling. When ligaments stretch or tear, inflammation floods the area with fluid. After a typical ankle sprain, you can expect swelling and limited movement for the first two weeks. Walking usually returns to normal between two and four weeks, with swelling gradually reducing during that period. Full return to normal daily activities generally takes 8 to 12 weeks.
Other injuries that cause localized swelling include fractures, tendon tears, and stress injuries from overuse. Infections like cellulitis, a bacterial skin infection, can also produce swelling along with redness, warmth, and pain. Gout, which commonly strikes the big toe joint, causes intense swelling and pain that comes on suddenly.
Pregnancy-Related Swelling
Some degree of ankle and foot swelling is normal during pregnancy, especially in the third trimester. The growing uterus puts pressure on the veins that return blood from the legs, and hormonal changes cause the body to retain more fluid.
What’s not normal is sudden swelling, particularly in the face and hands, after 20 weeks of pregnancy. This can be a sign of preeclampsia, a serious condition marked by high blood pressure and potential organ damage. Because headaches, nausea, and general aches are common pregnancy complaints, it can be hard to distinguish preeclampsia from routine discomfort, especially during a first pregnancy. Sudden puffiness that looks different from the gradual ankle swelling you’ve been experiencing warrants a prompt call to your provider.
How to Check the Severity
You can get a rough sense of how significant your swelling is with a simple test: press your thumb firmly into the swollen area for about five seconds, then release. If a visible dent remains, you have what’s called pitting edema. How deep the pit is and how long it takes to bounce back tells you the severity.
A shallow 2-millimeter indent that rebounds immediately is Grade 1, the mildest form. A 3 to 4 mm pit that fills back in within 15 seconds is Grade 2. Grade 3 leaves a 5 to 6 mm pit that takes up to 60 seconds to recover. Grade 4, the most severe, produces an 8 mm dent that can take two to three minutes to fill back in. Grade 3 or 4 pitting edema generally indicates a more serious underlying cause that needs medical evaluation.
Warning Signs That Need Urgent Attention
Most causes of swollen feet and ankles are manageable, but a few are genuinely dangerous. A blood clot in a deep leg vein (DVT) causes swelling in one leg along with pain or tenderness, warmth, and redness or discoloration. DVT requires prompt medical attention because part of the clot can break off and travel to the lungs, a life-threatening condition called pulmonary embolism.
Signs that a clot has reached the lungs include difficulty breathing, a faster or irregular heartbeat, chest pain that worsens when you breathe deeply or cough, coughing up blood, and feeling faint. This is a medical emergency.
Other combinations that warrant quick evaluation: swelling in both legs with new shortness of breath (possible heart failure), swelling with fever and spreading redness (possible infection), and the sudden onset of swelling during pregnancy with headache or vision changes (possible preeclampsia).
Reducing and Managing Swelling
For mild or occasional swelling, several strategies can help move fluid out of your lower legs. Elevating your feet above heart level for 15 to 20 minutes a few times a day uses gravity in your favor. Regular movement, even just flexing your ankles or taking short walks, activates your calf muscles and helps pump blood upward. Cutting back on sodium reduces the amount of fluid your body retains.
Compression stockings apply steady pressure to your legs and prevent fluid from accumulating. They come in different pressure levels: low compression (under 20 mmHg) works for mild swelling and tired legs, medium compression (20 to 30 mmHg) is typical for moderate edema and venous insufficiency, and high compression (above 30 mmHg) is used for more severe cases and usually requires a fitting or prescription.
When swelling is caused by an underlying condition like heart failure, kidney disease, or venous insufficiency, treating that root cause is what ultimately controls the edema. Persistent swelling that doesn’t improve with elevation and basic measures, or swelling that’s getting progressively worse over weeks, points to something that needs a diagnosis rather than just symptom management.