Swollen feet happen when excess fluid builds up in the tissue beneath your skin, usually because something has disrupted the normal balance of how fluid moves in and out of your blood vessels. The medical term is peripheral edema, and it ranges from completely harmless (you stood all day) to a signal that your heart, kidneys, or veins need attention. The cause usually becomes clear once you consider the pattern: whether one foot or both are swollen, how quickly it appeared, and what else is going on in your body.
How Fluid Ends Up in Your Feet
Your circulatory system constantly pushes fluid out of tiny blood vessels and pulls it back in. This works because of a balance between pressure inside the vessel and proteins in your blood that act like a sponge, drawing fluid back. When that balance tips, fluid leaks into the surrounding tissue and pools wherever gravity pulls it, which for most of your waking hours means your feet and ankles.
Five things can tip that balance: pressure inside blood vessels gets too high, the vessel walls become too leaky, blood proteins drop too low (so fluid isn’t pulled back in), the tissue outside the vessels holds onto extra fluid, or the lymphatic system that normally drains excess fluid can’t keep up. Most causes of swollen feet involve one or more of these mechanisms.
Common Everyday Causes
The most frequent reason for puffy feet is simply spending too long in one position. Sitting at a desk, riding in a car for hours, or standing on a hard floor all day lets gravity pull fluid downward faster than your body can push it back up. Walking activates calf muscles that squeeze blood upward through your veins, so the moment you stop moving, that pump stalls.
Eating a lot of salt is another common trigger. Sodium causes your body to hold onto water to keep the concentration of your blood balanced. The World Health Organization recommends staying under 2,000 mg of sodium per day (about one teaspoon of table salt), but most people consume well above that, especially from processed and restaurant food. A single salty meal can produce noticeable puffiness the next morning.
Heat plays a role too. In warm weather, blood vessels near the skin dilate to release heat, which increases pressure inside the capillaries and pushes more fluid out into surrounding tissue. This is why your shoes might feel tight on a hot afternoon even though nothing else has changed.
Medications That Cause Swelling
Several widely prescribed drugs list foot swelling as a side effect. Blood pressure medications called calcium channel blockers (amlodipine and nifedipine are among the most common) cause the small arteries feeding your capillaries to relax and widen. That widens the inflow pipe without widening the outflow, so pressure builds inside the capillary and fluid gets pushed into the tissue. This type of swelling is dose-dependent, meaning higher doses cause more puffiness.
Diabetes medications in the thiazolidinedione class (pioglitazone is the most common) cause swelling through a different route. They make blood vessel walls more permeable and cause the kidneys to hold onto extra sodium and water. NSAIDs like ibuprofen and naproxen can do something similar by reducing how efficiently the kidneys excrete sodium. Steroids, some antidepressants, and hormone therapies including estrogen and testosterone can also contribute.
If your swelling started shortly after beginning a new medication, that timing is a strong clue. Don’t stop the drug on your own, but it’s worth a conversation with your prescriber about alternatives.
Heart, Kidney, and Liver Problems
Swelling in both feet that develops gradually and worsens over weeks can be a sign of an organ struggling to do its job. In heart failure, the heart can’t pump blood forward efficiently, so it backs up in the veins of the legs and feet. The swelling tends to worsen throughout the day and improve overnight when you’re lying flat. Other signs include shortness of breath, fatigue, and waking up at night needing to catch your breath.
Kidney disease causes swelling differently. When the kidneys can’t filter properly, sodium and water accumulate in the body. You might also notice puffiness around your eyes in the morning, foamy urine, or changes in how often you urinate. Liver disease, particularly cirrhosis, reduces the liver’s production of albumin, a blood protein that holds fluid inside your vessels. Without enough albumin, fluid seeps out into tissue. Liver-related swelling often shows up in the abdomen as well as the legs.
In all three cases, swelling in both feet that persists for more than a few days, especially alongside other symptoms, warrants a medical evaluation.
Venous Insufficiency and Varicose Veins
Your leg veins contain one-way valves that keep blood moving upward toward the heart. Over time, these valves can weaken or fail, a condition called chronic venous insufficiency. When valves stop closing properly, blood flows backward and pools in the lower legs, increasing pressure inside the veins. That elevated pressure forces fluid out into the surrounding tissue.
This kind of swelling builds slowly over months or years. You might also notice varicose veins, a feeling of heaviness or aching in your legs, itchy skin around the ankles, or brownish discoloration on the lower legs. It’s more common in people over 50, those who have been pregnant, and anyone whose job requires prolonged standing. It’s not dangerous in itself, but severe, untreated cases can eventually lead to skin breakdown and ulcers near the ankles.
Pregnancy-Related Swelling
Some foot swelling during pregnancy is completely normal, especially in the third trimester. The growing uterus compresses veins in the pelvis, slowing the return of blood from the legs, and the body’s blood volume increases by nearly 50 percent.
What’s not normal is sudden swelling, particularly in the face and hands, which can signal preeclampsia. This condition involves high blood pressure and signs of organ stress, most commonly excess protein in the urine. It typically appears after 20 weeks and can escalate quickly. Sudden puffiness, severe headaches, vision changes, or upper abdominal pain during pregnancy all warrant immediate medical attention.
One Swollen Foot Is Different
When only one foot or leg swells, the concern shifts. A blood clot in a deep leg vein, called deep vein thrombosis (DVT), typically affects one side. Along with swelling, you might notice pain or cramping (often starting in the calf), warmth in the affected leg, and skin that looks red or purple. Some DVTs cause no symptoms at all.
DVT is more likely after surgery, long flights, extended bed rest, or in people taking hormonal birth control. It becomes an emergency if the clot breaks loose and travels to the lungs, causing a pulmonary embolism. Warning signs of that include sudden shortness of breath, chest pain that worsens when you breathe deeply, a rapid pulse, dizziness, or coughing up blood.
Other causes of one-sided swelling include an injury you might not remember (a minor sprain), an infection in the skin or tissue (cellulitis), or a blocked lymph node on that side.
How Doctors Assess Swelling
When you press a swollen area and a dent stays behind for a few seconds, that’s called pitting edema. Clinicians grade it on a 1 to 4 scale based on how deep the pit is and how long it takes to rebound. Grade 1 leaves a shallow 2 mm indent that bounces back immediately. Grade 4 leaves an 8 mm pit that takes two to three minutes to fill back in. Higher grades generally indicate more fluid accumulation and point toward a systemic cause rather than just a long day on your feet.
Your doctor will also ask about the timeline (sudden versus gradual), whether it’s one leg or both, what medications you take, and whether you have other symptoms like shortness of breath or changes in urination. Blood work and sometimes an ultrasound of the legs or heart help narrow the diagnosis.
What You Can Do About It
For mild, everyday swelling, the simplest fix is movement and elevation. Walking for even five minutes activates the calf muscle pump that pushes blood upward. When sitting, propping your feet above heart level for 15 to 20 minutes helps fluid drain back into circulation. Cutting sodium below 2,000 mg per day can make a noticeable difference within a few days.
Compression socks apply gentle, graduated pressure that helps veins move blood upward. For mild swelling, 15 to 20 mmHg pressure is usually enough. People with chronic venous insufficiency or persistent edema often benefit from 20 to 30 mmHg or higher, though stronger compression should be fitted based on a clinical assessment. Put them on first thing in the morning before swelling has a chance to build.
Staying well hydrated actually helps rather than hurts. When you’re dehydrated, your body holds onto more sodium, which worsens fluid retention. Regular exercise, maintaining a healthy weight, and avoiding long stretches of sitting or standing all reduce the frequency and severity of swelling episodes.
For swelling caused by an underlying condition like heart failure, venous insufficiency, or kidney disease, managing the root problem is what ultimately controls the swelling. Treatment looks different for each condition, but in all cases, the swelling itself is a signal, not the disease.