Swelling in the feet and ankles happens when fluid leaks out of small blood vessels and gets trapped in the surrounding tissue. This is called peripheral edema, and it has dozens of possible causes ranging from standing too long on a hot day to serious organ problems. The key to figuring out what’s behind your swelling is whether it affects one leg or both, how quickly it appeared, and what other symptoms came with it.
How Fluid Ends Up Trapped in Your Feet
Your body constantly moves fluid between your bloodstream and the tissue around it. Two main forces keep this exchange balanced: the pressure of blood pushing fluid out through vessel walls, and proteins in your blood (especially one called albumin) pulling fluid back in. When either of these forces shifts, fluid accumulates in the lowest parts of your body, which is why feet and ankles are usually the first place you notice it.
Gravity plays a major role. Sitting or standing for hours lets blood pool in the veins of your lower legs, increasing pressure and pushing more fluid into surrounding tissue. This is why long flights, desk jobs, and hot weather are the most common triggers for mild, temporary swelling. Moving your calf muscles acts as a pump that pushes blood back up toward your heart, so inactivity stalls the whole system.
Heart, Kidney, and Liver Problems
When swelling shows up in both feet and persists day after day, it can signal that a major organ isn’t doing its job. Congestive heart failure is one of the most common serious causes. When the heart can’t pump blood efficiently, it backs up in the veins of the legs, ankles, and feet. That backup raises pressure inside the veins and forces fluid out into tissue. Heart failure can also cause swelling in the abdomen and fluid buildup in the lungs, which feels like shortness of breath, especially when lying flat.
Kidney disease works through a different mechanism. Healthy kidneys filter waste while keeping proteins like albumin in the blood. When kidney filters are damaged, albumin spills into the urine. With less albumin in the bloodstream, there’s less pulling force to draw fluid back into your vessels, so it pools in your tissue instead. This protein loss is a hallmark of a condition called nephrotic syndrome, which causes puffy swelling that often starts around the eyes in the morning and settles into the feet and ankles by evening.
Liver disease, particularly cirrhosis, causes a similar problem. The liver produces albumin, so when it’s scarred and failing, albumin levels drop and fluid escapes into tissue. Liver-related swelling often appears alongside a swollen abdomen from fluid accumulation there.
Venous Insufficiency
Veins in your legs have one-way valves that keep blood moving upward against gravity. Over time, these valves can weaken or fail, a condition called chronic venous insufficiency. Blood pools in the lower legs, pressure builds, and fluid seeps into surrounding tissue. This is one of the most common causes of persistent foot and ankle swelling, particularly in people over 50.
Without treatment, venous insufficiency progresses through recognizable stages. Early on, you may only notice swelling that worsens through the day and improves overnight. As pressure continues to damage the smallest blood vessels, capillaries burst and release iron-containing pigments into the skin, giving it a reddish-brown discoloration, typically around the inner ankle. In advanced stages, scar tissue forms in the lower leg, trapping fluid permanently and making the calf feel hard. The skin becomes fragile, and open sores called venous ulcers can develop. These ulcers are slow to heal and prone to infection. Catching venous insufficiency early, before skin changes begin, makes treatment far more effective.
Medications That Cause Swelling
Foot and ankle swelling is a surprisingly common side effect of everyday medications. If your swelling started within a few weeks of beginning a new drug, the medication itself may be the cause. This type of swelling is typically soft, affects both feet equally, and resolves within days of stopping the drug.
The most frequent culprits are blood pressure medications called calcium channel blockers, which work by relaxing artery walls. That relaxation increases blood flow into tiny capillaries faster than the veins can drain it, and fluid leaks into tissue. Hormone-related medications, including estrogen, progesterone, testosterone, and steroids like prednisone, cause the kidneys to hold onto sodium and water, which increases overall fluid volume. Diabetes medications in the thiazolidinedione class work the same way. Even over-the-counter anti-inflammatory painkillers (NSAIDs like ibuprofen) can promote fluid retention, though this is less common.
Blood Clots: When One Leg Swells
Swelling that appears in only one leg deserves immediate attention. A deep vein thrombosis (DVT), a blood clot in one of the deep veins of the leg, blocks blood from draining properly and causes swelling, often accompanied by pain or cramping that starts in the calf. The skin over the affected area may feel warm and look red or purple.
DVT is dangerous not because of the swelling itself, but because the clot can break loose and travel to the lungs, causing a pulmonary embolism. Warning signs of that complication include sudden shortness of breath, chest pain that worsens with deep breaths or coughing, a rapid pulse, dizziness, or coughing up blood. These symptoms require emergency care. Risk factors for DVT include recent surgery, long periods of immobility (like a hospital stay or long-haul flight), cancer, pregnancy, and use of hormonal birth control.
Swelling During Pregnancy
Some ankle swelling during pregnancy is completely normal, especially in the third trimester. The growing uterus puts pressure on pelvic veins, slowing blood return from the legs. Hormonal shifts also cause the body to retain more fluid.
The concern is when swelling signals preeclampsia, a serious pregnancy complication. Preeclampsia involves blood pressure reaching 140/90 or higher, along with protein in the urine or signs of organ stress. Severe preeclampsia pushes blood pressure to 160/110 or above. A woman with mild preeclampsia may notice only subtle puffiness in her hands or feet, which is easy to dismiss as typical pregnancy swelling. The distinguishing features are rapid onset (swelling that appears suddenly rather than gradually), swelling in the face and hands rather than just the feet, headaches, vision changes, and upper abdominal pain. Blood pressure monitoring at prenatal visits is the primary way preeclampsia gets caught.
How Pitting Edema Is Graded
When you press a swollen area with your finger and the dent stays, that’s called pitting edema. Doctors grade it on a 1 to 4 scale based on how deep the dent is and how long it takes to bounce back. Grade 1 leaves a shallow 2-millimeter pit that rebounds immediately. Grade 2 creates a 3 to 4 millimeter pit that fills back in within 15 seconds. Grade 3 produces a 5 to 6 millimeter pit that takes up to a minute to rebound. Grade 4 leaves an 8-millimeter dent that can take two to three minutes to flatten out.
Higher grades generally indicate more fluid accumulation and a greater likelihood that something systemic is going on. If you can push your thumb into your ankle and the indent lingers for more than a few seconds, that’s worth bringing up with a healthcare provider.
Reducing and Managing Swelling
For mild or occasional swelling, simple changes can make a real difference. Elevating your feet above heart level for 15 to 20 minutes several times a day helps gravity work in your favor. Compression socks apply steady pressure that keeps fluid from pooling. Regular walking, even short walks, activates the calf muscle pump that pushes blood back up toward the heart.
Sodium plays a direct role in fluid retention because your body holds onto water to keep sodium levels balanced. For people managing heart failure, guidelines from the Heart Failure Society of America recommend keeping sodium intake between 2,000 and 3,000 milligrams per day, with a stricter limit of under 2,000 milligrams for moderate to severe cases. Even without heart failure, cutting back on sodium can reduce swelling. Most excess sodium comes from processed and restaurant food rather than the salt shaker, so reading labels is more effective than simply not adding salt at the table.
When swelling is caused by an underlying condition, treating the root cause is what ultimately controls it. Diuretics (water pills) can provide relief by helping the kidneys flush excess fluid, but they address the symptom, not the source. If your swelling is persistent, worsening, affects only one side, or comes with shortness of breath, chest pain, or skin changes, those patterns point toward causes that need medical evaluation rather than home management.