Swollen feet and ankles happen when fluid builds up in the tissue beneath your skin, and the causes range from standing too long to serious organ problems. Whether the swelling affects one foot or both, and whether it came on suddenly or gradually, tells you a lot about what’s behind it.
Your body constantly moves fluid between your bloodstream and surrounding tissues. Swelling occurs when more fluid leaks out of tiny blood vessels than your lymphatic system can drain back. This can happen because pressure inside the vessels gets too high, because proteins that normally hold fluid in the bloodstream drop too low, or because the vessels themselves become leaky from inflammation or injury.
Swelling in Both Feet vs. One Foot
The single most useful clue is whether the swelling is in one leg or both. Swelling in both feet and ankles usually points to a body-wide issue: heart failure, kidney disease, liver problems, medication side effects, or pregnancy. Swelling in just one foot or ankle is more likely caused by something local, like a blood clot, an injury, an infection, or damaged veins in that leg.
Timing matters too. Sudden swelling in one leg that comes with pain, warmth, or redness could signal a deep vein thrombosis (a blood clot in a deep leg vein), which needs urgent attention. Gradual swelling that worsens over weeks or months in both legs is more characteristic of chronic venous insufficiency, heart failure, or a medication effect.
Chronic Venous Insufficiency
This is one of the most common reasons people develop persistent ankle swelling. The veins in your legs contain one-way valves that push blood upward toward the heart. When those valves weaken or get damaged, blood pools in the lower legs instead of circulating efficiently. The result is swelling that’s typically worse at the end of the day, after hours of standing or sitting, and improves overnight when you lie flat.
Over time, chronic venous insufficiency can cause more than just puffiness. You may notice a feeling of heaviness, aching, cramping, or tiredness in your legs. Varicose veins often accompany it. If left unmanaged for years, the skin around the ankles can darken, become dry and irritated, or even develop ulcers. Up to 50% of people who’ve had a deep vein thrombosis develop a version of this condition within one to two years.
Heart, Kidney, and Liver Problems
When swelling shows up in both legs and doesn’t have an obvious explanation, it can be an early sign of organ dysfunction.
In congestive heart failure, one or both of the heart’s lower chambers lose their ability to pump blood efficiently. Blood backs up in the veins, and pressure builds in the legs, ankles, and feet, forcing fluid into surrounding tissue. This kind of swelling often comes with shortness of breath, fatigue, or difficulty lying flat at night.
Kidney disease causes the body to retain fluid and salt that would normally be filtered out. Swelling linked to kidney problems tends to show up in the legs and around the eyes. In nephrotic syndrome, a specific type of kidney damage, the kidneys leak protein into the urine. That lowers protein levels in the blood, which reduces the blood’s ability to pull fluid back in from tissues, and swelling follows.
Liver cirrhosis disrupts the production of albumin, the main protein responsible for keeping fluid inside your blood vessels. As albumin levels drop, fluid seeps into the abdomen and legs. Swelling from liver disease is often accompanied by a noticeably distended belly.
Medications That Cause Swelling
Medication side effects are among the most common and most overlooked causes of swollen ankles. Calcium channel blockers, a widely prescribed class of blood pressure drugs, cause peripheral edema in up to 70% of people taking them. These drugs relax blood vessel walls, which increases pressure in the small vessels of the legs and pushes fluid into surrounding tissue. The swelling isn’t caused by excess fluid in the body, so water pills often don’t help much.
Other medications known to cause ankle and foot swelling include:
- Anti-inflammatory painkillers (NSAIDs): ibuprofen and similar drugs cause the kidneys to retain sodium and water
- Certain diabetes medications: particularly the thiazolidinedione class
- Steroids: both corticosteroids and hormonal medications like estrogen and testosterone
- Some antidepressants and nerve pain drugs
If you notice swelling that started after beginning a new medication, that connection is worth raising with whoever prescribed it. Switching to a different drug in the same class can sometimes resolve the problem entirely.
Pregnancy-Related Swelling
Some degree of foot and ankle swelling is normal during pregnancy, especially in the third trimester. The growing uterus puts pressure on veins that return blood from the legs, and hormonal shifts cause the body to retain more fluid. This type of swelling tends to be mild, develops gradually, and affects both feet.
What’s not normal is sudden, significant swelling, particularly in the face and hands. This can be a warning sign of preeclampsia, a serious pregnancy complication that usually begins after 20 weeks. Preeclampsia involves dangerously high blood pressure and can progress quickly, so sudden puffiness during pregnancy warrants prompt medical evaluation.
Prolonged Sitting and Standing
Gravity is constantly pulling fluid downward, and your calf muscles act as a pump to push blood back up toward your heart. When you sit at a desk for hours, take a long flight, or stand in one position all day, that pump barely activates. Fluid accumulates in the lowest point: your feet and ankles. This type of swelling is harmless in most cases and resolves with movement or elevation, but it can become a recurring nuisance for people with sedentary jobs or limited mobility.
Lymphedema
Your lymphatic system is a network of vessels that drains excess fluid from tissues and returns it to the bloodstream. When that network is damaged or blocked, fluid accumulates, causing a type of swelling called lymphedema. This can happen after surgery (especially cancer surgery that involves removing lymph nodes), after radiation therapy, or from infections that scar the lymphatic vessels. In some cases, lymphedema has no identifiable cause.
Lymphedema swelling feels different from other types. It tends to be firmer, doesn’t pit as easily when you press on it (though early-stage lymphedema can pit), and doesn’t improve much with elevation alone. It often affects one leg more than the other and can worsen progressively without treatment.
Managing Mild Swelling at Home
When swelling is mild and tied to lifestyle factors rather than organ disease, a few strategies help. Elevating your legs above the level of your heart several times a day lets gravity work in your favor, draining fluid back toward your core. Even 15 to 20 minutes of elevation can make a noticeable difference.
Reducing sodium intake helps because salt causes your body to retain water. Most people consume far more sodium than they need, and cutting back on processed foods is the easiest way to lower it. Regular movement, even short walks or calf raises at your desk, keeps the muscle pump in your legs active.
Compression socks apply graduated pressure to your lower legs, helping push fluid upward. For everyday use or travel, 15 to 20 mmHg is a comfortable starting range. For varicose veins, moderate swelling, or post-surgery recovery, 20 to 30 mmHg provides firmer support. They work best when you put them on in the morning before swelling sets in.
Signs That Swelling Needs Urgent Attention
Most ankle swelling is not an emergency, but some patterns signal something serious. Sudden swelling in one leg, especially with pain, warmth, or redness in the calf, could indicate a blood clot. Swelling paired with chest pain or sudden shortness of breath suggests the possibility that a clot has traveled to the lungs or that the heart is failing acutely. Swelling that appears rapidly alongside reduced urine output may point to acute kidney failure. And during pregnancy, sudden swelling in the face and hands with headache or vision changes raises concern for preeclampsia. Any of these combinations calls for immediate medical evaluation.