Swollen feet result from fluid accumulating in the tissues of your lower extremities, and the list of possible causes ranges from eating too much salt to serious organ disease. The medical term is edema, and whether it affects one foot or both is one of the most important clues to what’s driving it. Understanding the most common triggers can help you figure out whether your swelling is a temporary nuisance or something that needs medical attention.
Too Much Sodium or Too Little Movement
The simplest explanation for swollen feet is also the most common: your body is holding onto extra water. Sodium is the main driver here. Water follows sodium in the body, so when you eat a salty meal, your blood volume temporarily increases and fluid gets pushed into the surrounding tissues, especially in the feet and ankles where gravity pulls it. The general recommendation is to stay under 2,300 milligrams of sodium per day, and closer to 1,500 milligrams if you have high blood pressure or heart disease. For context, a single fast-food meal can easily exceed 2,000 milligrams.
Sitting or standing in one position for hours has a similar effect. Without the pumping action of your leg muscles to push blood back up toward your heart, fluid pools in your lower legs. Long flights, desk jobs, and car rides are classic triggers. Simply getting up and walking around every hour or two makes a noticeable difference.
One Foot vs. Both Feet: Why It Matters
Swelling in just one foot points to a local problem. The most urgent concern is a deep vein thrombosis (DVT), a blood clot in the leg. Once a clot is ruled out, the most common explanations break down roughly like this: about 40% of cases involve a muscle strain, tear, or twisting injury; around 7% stem from vein problems in that leg; about 5% come from a fluid-filled cyst behind the knee (called a Baker’s cyst); and about 3% are caused by a skin infection. In roughly a quarter of cases, no clear cause is found.
When both feet swell at the same time, the cause is usually systemic, meaning something affecting your whole body. The most common culprits are heart failure, kidney disease, medications, or chronic vein problems. Bilateral swelling that comes on suddenly warrants prompt evaluation, particularly if it’s paired with shortness of breath.
Heart and Kidney Disease
Congestive heart failure is one of the more serious causes of swollen feet. When the heart’s lower chambers can’t pump blood efficiently, blood backs up in the veins of the legs, ankles, and feet. The resulting swelling tends to worsen throughout the day and improve overnight when you’re lying flat. It often comes alongside fatigue, shortness of breath, and rapid weight gain from fluid retention.
Kidney disease causes swelling through a different path. Damaged kidneys struggle to remove excess fluid and salt from the blood, so the extra volume has to go somewhere. In a condition called nephrotic syndrome, the kidneys also leak protein into the urine, which lowers protein levels in the blood. Since blood proteins normally act like sponges that keep fluid inside your vessels, losing them allows fluid to seep into surrounding tissue.
Chronic Venous Insufficiency
Your veins have tiny one-way valves that keep blood moving upward against gravity. When those valves weaken or fail, blood flows backward and pools in the lower legs, a condition called chronic venous insufficiency (CVI). It’s the most common cause of chronic swelling in both legs.
CVI often develops after a previous blood clot damages the valves in the deep veins. The backward flow of blood raises pressure inside the smallest blood vessels, causing them to stretch, leak, and push fluid into the surrounding tissue. Over time, this persistent pressure causes visible changes: the skin around the ankles may darken (from leaked red blood cells breaking down), the tissue underneath can harden and feel woody, and in advanced cases, open sores or ulcers develop near the ankle. These skin changes are a hallmark that distinguishes CVI from other causes of swelling.
Lymphedema
Your lymphatic system acts as a drainage network, collecting excess fluid from tissues and returning it to the bloodstream. When that system is blocked or damaged, fluid builds up, most often in an arm or leg. This is lymphedema, and it behaves differently from other types of swelling.
Lymphedema typically starts on the top of the foot and progresses upward. In early stages, the swelling is soft and doughy, and it goes down when you elevate your leg. As it advances, fat cells enlarge in response to the trapped fluid, and the swelling no longer improves with elevation. In its most severe stage, the skin thickens, develops a dimpled “orange peel” texture, and eventually becomes hard and leathery. A classic sign of advanced lymphedema is the inability to pinch a fold of skin at the base of the second toe, known as Stemmer’s sign.
Common causes include surgery or radiation therapy that damages lymph nodes, particularly in the groin or pelvis. This is why lymphedema sometimes appears months or years after cancer treatment.
Medications That Cause Swelling
Several widely prescribed medications list foot and ankle swelling as a side effect. Calcium channel blockers, a class of blood pressure drugs, are among the most common offenders. At standard doses, between 1% and 15% of people develop ankle swelling. At high doses taken long-term, that number can climb above 80%. The swelling happens because these drugs relax blood vessel walls, which allows more fluid to leak into surrounding tissues.
Adding a second type of blood pressure medication (an ACE inhibitor or ARB) reduces the swelling risk by about 38% compared to taking a calcium channel blocker alone. In one trial, swelling dropped from nearly 19% with the calcium channel blocker alone to under 8% when it was combined with another agent.
Other drug classes linked to foot swelling include anti-inflammatory painkillers (NSAIDs), hormone therapies including estrogen and testosterone, certain diabetes medications, and corticosteroids. If you notice new swelling after starting a medication, that connection is worth raising with your prescriber.
Injuries and Sprains
A twisted ankle or a stress fracture triggers an immediate inflammatory response, flooding the injured area with fluid, immune cells, and nutrients needed for repair. This type of swelling is usually obvious because it follows a specific event, hurts, and is limited to one foot or ankle.
For a typical ankle sprain, noticeable improvement in swelling and movement happens within the first two weeks. By two to four weeks, walking usually returns to normal, movement is nearly fully restored, and swelling continues to fade. More severe injuries, like fractures, follow a longer timeline, but the general pattern is the same: swelling peaks in the first 48 to 72 hours and then gradually resolves.
Pregnancy Swelling and Warning Signs
Some degree of foot and ankle swelling is normal during pregnancy, particularly in the third trimester. Hormonal shifts cause the body to retain more sodium and water, and the growing uterus puts pressure on pelvic veins, slowing the return of blood from the legs.
The concern is when swelling changes character. A sudden increase in swelling, especially if it spreads to your hands and face, can signal preeclampsia, a serious pregnancy complication involving high blood pressure. Other warning signs that accompany preeclampsia include persistent headaches, blurry vision or visual changes, pain in the upper right side of the abdomen, nausea, confusion, and decreased urine output. Blood pressure above 140/90 during pregnancy is the key clinical red flag. Preeclampsia can develop even without dramatic swelling, so blood pressure monitoring throughout pregnancy is essential.
Reducing and Managing Swelling
For mild, everyday swelling not tied to a serious medical condition, a few consistent habits make a real difference. Elevating your legs above the level of your heart for about 15 minutes, three to four times a day, helps fluid drain back toward your core. This is most effective when you lie down and prop your feet on pillows rather than simply resting them on an ottoman.
Compression stockings apply graduated pressure to your legs, squeezing tightest at the ankle and gradually loosening up the calf. For general swelling and comfort, stockings in the 15 to 20 mmHg range provide meaningful relief. For chronic venous disease with persistent edema, guidelines recommend 20 to 40 mmHg below-knee stockings. Higher-pressure garments (40 mmHg and above) are available for more severe cases but typically require a fitting.
Cutting back on sodium, staying physically active, and avoiding long periods of sitting or standing address the most common everyday triggers. Walking is particularly effective because the calf muscles act as a pump, compressing the veins and pushing blood upward with each step. Even gentle ankle circles and calf raises while seated can help when you’re stuck at a desk or on a plane.