Swollen feet happen when fluid leaks out of tiny blood vessels and collects in the surrounding tissue faster than your lymphatic system can drain it away. This is called edema, and it ranges from a harmless response to gravity and salt intake all the way to a signal that your heart, kidneys, or veins need attention. The cause usually depends on whether the swelling is in one foot or both, how quickly it appeared, and what other symptoms come with it.
How Fluid Ends Up in Your Feet
Your blood vessels constantly filter fluid in and out of surrounding tissues. Two forces keep this exchange balanced: the pressure of blood pushing fluid out through capillary walls, and proteins in your blood pulling fluid back in. When something raises the outward pressure or lowers the inward pull, more fluid escapes into the tissue than your body can reabsorb. Gravity pulls that excess fluid downward, which is why feet and ankles bear the brunt.
Your lymphatic system acts as a backup drainage network, slowly returning leaked fluid to your bloodstream. But it has a limited capacity. When the volume of escaped fluid outpaces what the lymphatic vessels can handle, the tissue swells visibly. That’s true whether the root cause is sitting on a long flight or a failing heart valve.
The Most Common Everyday Causes
For many people, swollen feet at the end of the day have a straightforward explanation. Prolonged sitting or standing lets gravity pool blood in the lower legs, raising pressure in the veins and pushing fluid into the tissue. Long car rides, desk jobs, and flights are classic triggers. The swelling typically goes down overnight once you’re lying flat and gravity is no longer working against you.
High sodium intake is another frequent culprit. Salt causes your body to hold onto water, increasing the total volume of fluid in your blood vessels and raising the pressure that forces fluid out into tissue. The American Heart Association recommends staying under 1,500 mg of sodium per day for the general population. For context, a single fast-food meal can contain more than that. Cutting back on processed foods, canned soups, and restaurant meals often makes a noticeable difference within days.
Heat also plays a role. In warm weather, your blood vessels dilate to help release body heat, which lowers the pressure that keeps fluid inside the vessels. This is why feet that seem fine in winter puff up in the summer.
Medications That Cause Swelling
Several widely prescribed drugs list foot and ankle swelling as a common side effect. Calcium channel blockers, a type of blood pressure medication, are among the most frequent offenders. Amlodipine, one of the most commonly prescribed versions, causes at least some foot or ankle swelling in nearly half the people who take it.
Other medications known to trigger swelling include:
- NSAIDs like ibuprofen and naproxen, which cause the body to retain sodium and water
- Hormone medications including estrogen, progesterone, testosterone, and corticosteroids
- Gabapentin and pregabalin, often prescribed for nerve pain or seizures
- Other blood pressure drugs such as beta blockers, clonidine, and hydralazine
- Pioglitazone, a diabetes medication
- Pramipexole, used for Parkinson’s disease
- Certain antidepressants, particularly MAOIs
If your feet started swelling after beginning a new medication or changing a dose, that connection is worth raising with whoever prescribed it. Switching to a different drug in the same class often resolves the problem.
Venous Insufficiency
Veins in your legs contain one-way valves that push blood upward toward your heart, fighting gravity with every step. When those valves weaken or become damaged, blood flows backward and pools in the lower legs. This is called chronic venous insufficiency, and it’s one of the most common causes of persistent foot swelling, especially in people over 50.
The pooling blood raises pressure inside the veins, which forces more fluid into the surrounding tissue. Over time, this sustained pressure can burst the tiniest capillaries, causing brownish skin discoloration around the ankles. In severe cases, the trapped fluid triggers scar tissue formation in the skin and deeper tissue, which then traps even more fluid in a worsening cycle. Skin ulcers can eventually develop if the condition goes untreated.
Risk factors include a history of blood clots, varicose veins, obesity, pregnancy, and jobs that require long hours of standing. The swelling typically worsens throughout the day and improves overnight.
Heart, Kidney, and Liver Conditions
When your heart can’t pump blood efficiently, blood backs up in the veins, raising the pressure that pushes fluid into your tissues. At the same time, reduced blood flow to the kidneys triggers them to retain extra sodium and water in an attempt to boost blood volume. This creates a feedback loop: the heart struggles, the kidneys hold onto fluid, blood volume increases, and the swelling gets worse. Foot and ankle swelling that comes with shortness of breath, fatigue, or difficulty lying flat at night can point to heart failure.
Kidney disease disrupts the equation from the other side. Damaged kidneys lose the ability to filter excess fluid and may also leak protein into the urine. Since blood proteins are what pull fluid back into your vessels, losing them means more fluid stays trapped in the tissue. Liver disease, particularly cirrhosis, causes a similar protein deficit because the liver is where many of those proteins are made.
These systemic causes typically produce swelling in both feet and legs rather than just one, and the swelling tends to develop gradually over weeks rather than appearing overnight.
Swelling During Pregnancy
Mild foot and ankle swelling during pregnancy is normal, especially in the third trimester. Your blood volume increases by nearly 50% to support the baby, and the growing uterus puts pressure on the veins that return blood from your legs. Most pregnancy-related swelling is harmless and resolves after delivery.
Certain patterns of swelling during pregnancy warrant immediate attention. Sudden swelling that quickly gets worse, particularly if paired with headaches or vision changes, can signal preeclampsia, a condition where blood pressure rises to dangerous levels. Swelling that appears suddenly in only one leg, especially if it’s painful or warm, could indicate a blood clot. Sudden puffiness in the face or hands is also a red flag that blood pressure may be climbing.
One Foot vs. Both Feet
Whether the swelling affects one foot or both is one of the most important clues to its cause. Swelling in both feet usually points to something systemic: too much salt, a medication side effect, prolonged sitting, or an underlying condition like heart failure, kidney disease, or venous insufficiency affecting both legs.
Swelling that appears suddenly in just one foot or leg is a different story. The most urgent concern is a deep vein thrombosis (DVT), a blood clot in a deep leg vein. A DVT typically causes swelling, warmth, redness, and pain in the affected leg. This is a medical emergency because the clot can break loose and travel to the lungs. Other causes of one-sided swelling include a sprained ankle, a localized infection, or a blocked lymph node on that side.
How to Check the Severity
You can get a rough sense of how much fluid has accumulated with a simple test: press your thumb firmly into the swollen area for about five seconds, then release. If the skin bounces back right away and leaves only a shallow dent of about 2 millimeters, the swelling is mild. If the dent is 3 to 4 millimeters deep and takes up to 15 seconds to refill, that’s moderate. A deeper pit of 5 to 6 millimeters that takes up to a minute to rebound, or an 8-millimeter pit that lingers for two to three minutes, indicates more significant fluid retention that needs medical evaluation.
What You Can Do at Home
For mild, everyday swelling, a few practical strategies make a real difference. Elevating your feet above the level of your heart for 15 to 30 minutes several times a day lets gravity work in your favor, draining fluid back toward your core. Lying on the couch with your feet propped on a stack of pillows works. Sitting in a recliner with your legs level doesn’t, because your feet need to be higher than your chest.
Compression socks apply graduated pressure that helps push fluid upward out of your feet and ankles. For mild swelling, socks rated at 15 to 20 mmHg provide gentle support and are sold over the counter. Moderate swelling often responds better to 20 to 30 mmHg, which is the most commonly recommended range for daily wear. Higher pressures of 30 to 40 mmHg are typically reserved for more significant conditions like chronic venous insufficiency or lymphedema and should be fitted with guidance from a clinician. Put compression socks on first thing in the morning before your feet have a chance to swell.
Reducing sodium intake, staying hydrated (which paradoxically helps your body release excess fluid rather than hoard it), and moving your feet and ankles regularly throughout the day all help keep fluid from settling. Even simple ankle circles or calf raises at your desk can activate the muscle pumps that push blood back toward your heart.
Persistent swelling that doesn’t improve with elevation and lifestyle changes, swelling that leaves deep pits when pressed, or swelling that comes with shortness of breath, chest pain, or skin changes is telling you something more is going on beneath the surface.