Swelling in the feet happens when excess fluid gets trapped in the tissues beneath your skin. The underlying cause can be as simple as sitting too long or eating a salty meal, or it can signal something more serious like heart failure, kidney disease, or a blood clot. Understanding the most common triggers helps you figure out whether your swelling is temporary or worth investigating further.
How Fluid Ends Up in Your Feet
Your body constantly moves fluid between your bloodstream and the tissues around it. This exchange stays balanced thanks to pressure inside your blood vessels, proteins in your blood that pull fluid back in, and a drainage network called the lymphatic system. Swelling occurs when any part of this system tips out of balance: pressure inside the vessels gets too high, proteins that hold fluid in the blood drop too low, vessel walls become too leaky, or drainage backs up.
Gravity makes feet and ankles the first place fluid collects. Blood returning from your lower legs has to travel upward against gravity, and the veins rely on one-way valves and calf muscle contractions to push it along. Anything that slows that return, from sitting in a car for hours to weakened vein valves, lets fluid pool in the lowest point of your body.
Vein Problems Are a Leading Cause
Chronic venous insufficiency is one of the most common reasons feet swell, especially in people over 50. The condition develops when the small one-way valves inside your leg veins stop closing properly. Normally these valves keep blood flowing upward toward the heart. When they fail, blood falls backward and pools in the lower legs, raising pressure inside the veins and forcing fluid into surrounding tissue.
Valve damage most often results from a previous blood clot (deep vein thrombosis), but it can also stem from inherited weakness in the vein walls, inflammation, or prolonged standing. Studies estimate that clinically significant vein disease affects roughly 60% of adults worldwide, though severe cases with skin changes or ulcers are far less common, occurring in about 1% of the population. Prevalence rises with age: one large screening study found venous insufficiency in 21% of men and 12% of women over age 50.
Varicose veins, visible bulging veins on the surface of the legs, are a related problem. They signal that superficial veins have stretched beyond the point where their valves can function, allowing high-pressure blood to flow backward into the surface system.
Heart Failure and Fluid Backup
When the right side of the heart becomes too weak to pump blood efficiently to the lungs, blood backs up in the veins throughout the body. That backup raises venous pressure, which pushes fluid out of the blood vessels and into surrounding tissues. The result is swelling in the legs, feet, and sometimes the abdomen.
Heart-related swelling tends to worsen throughout the day as you spend time upright, and it often improves overnight when you’re lying flat. It usually affects both feet equally. You might also notice shortness of breath, fatigue, or a feeling of fullness in your abdomen. If foot swelling appears alongside these symptoms, especially if it develops over days to weeks, it’s worth getting your heart checked.
Kidney Disease and Protein Loss
Your kidneys filter blood through tiny structures called glomeruli. When those filters are damaged, a protein called albumin leaks out of the blood and into the urine. Albumin normally acts like a sponge inside your blood vessels, pulling fluid back in and keeping it from leaking out. As albumin levels drop, fluid escapes into the tissues, causing swelling that often shows up first in the feet and ankles.
This pattern of protein loss is called nephrotic syndrome, and foot swelling is one of its hallmark signs. The swelling may also appear around the eyes, especially in the morning. If you notice puffy ankles alongside foamy urine (a sign of excess protein), that combination points toward a kidney issue.
Medications That Cause Swelling
Several common medications can trigger foot and ankle swelling as a side effect. The most well-known culprits are calcium channel blockers, a class of blood pressure drugs. These medications relax blood vessel walls, which can increase pressure in the small capillaries and push fluid into surrounding tissue. The incidence ranges from 1% to 15% of people taking standard doses, but at high doses taken long-term, ankle swelling can affect more than 80% of patients.
Other medications that commonly cause swelling include corticosteroids (like prednisone), certain diabetes drugs, hormone replacement therapy, and some antidepressants. If your feet started swelling around the time you began a new medication, that timing is an important clue. Don’t stop a prescribed medication on your own, but do bring it up with whoever prescribed it.
Salt, Prolonged Sitting, and Other Everyday Triggers
A high-sodium diet is one of the simplest explanations for mild foot swelling. Sodium causes your body to retain water, and the extra fluid tends to settle in your lower extremities. Most Americans consume between 2,750 and 7,000 milligrams of sodium per day. For people who already have heart or kidney problems, that level of intake directly worsens swelling. Even in otherwise healthy people, a particularly salty meal can cause noticeable puffiness in the feet and ankles the next morning.
For people with existing edema, clinical guidelines recommend keeping sodium intake between 1,375 and 1,800 milligrams per day, which is well below what most people eat. Cutting back on processed foods, restaurant meals, and packaged snacks makes the biggest difference, since those sources account for the majority of dietary sodium.
Prolonged sitting or standing also contributes. Long flights, desk jobs, and car rides all keep your calf muscles inactive, which means they aren’t pumping blood back up toward the heart. Hot weather compounds the effect because heat causes blood vessels to dilate, increasing fluid leakage into tissues.
Pregnancy-Related Swelling
Some degree of foot swelling is normal during pregnancy, particularly in the third trimester, as the body retains extra fluid and the growing uterus puts pressure on the veins returning blood from the legs. This type of swelling typically develops gradually and affects both feet.
What’s not normal is sudden swelling, particularly in the face and hands along with the feet. A rapid increase in swelling or unexplained weight gain can be a sign of preeclampsia, a serious blood pressure condition that develops after 20 weeks of pregnancy. Preeclampsia requires prompt medical attention. The key distinction is gradual versus sudden: slow, symmetric puffiness in the ankles is expected, while a rapid change warrants a call to your provider.
When Swelling Affects Only One Foot
Swelling that appears in just one foot or leg is a different situation from bilateral swelling and raises the concern of a blood clot, specifically a deep vein thrombosis (DVT). A DVT forms when blood clots inside one of the deep veins of the leg, blocking normal blood flow and causing fluid to accumulate below the blockage.
Along with one-sided swelling, a DVT often causes warmth, redness, and tenderness in the affected leg. The calf may feel tight or painful when you flex your foot upward. Risk factors include recent surgery, prolonged immobility (such as a long flight or hospital stay), cancer, pregnancy, and use of oral contraceptives. A DVT is a medical emergency because the clot can break loose and travel to the lungs. One-sided leg swelling that comes on quickly, especially with pain or redness, needs same-day evaluation.
Other causes of one-sided swelling include a sprained ankle, an infection in the foot or lower leg, or lymphatic damage on one side from surgery or radiation.
How Doctors Assess Swelling Severity
If you visit a doctor for foot swelling, one of the first things they’ll do is press a finger into the swollen area for a few seconds and then release. If the pressure leaves a visible dent that takes time to fill back in, that’s called pitting edema, and it’s graded on a 1-to-4 scale based on how deep the pit is and how long it takes to rebound:
- Grade 1: A shallow 2-millimeter dent that rebounds immediately
- Grade 2: A 3- to 4-millimeter dent that fills back in within 15 seconds
- Grade 3: A 5- to 6-millimeter dent that takes 15 to 60 seconds to rebound
- Grade 4: An 8-millimeter dent that persists for two to three minutes
Higher grades suggest more significant fluid accumulation and typically prompt further testing, such as blood work to check kidney and liver function, an ultrasound of the leg veins, or imaging of the heart. The pattern of swelling matters too. Both legs swelling symmetrically points toward a systemic cause like heart, kidney, or liver problems. One leg swelling alone raises suspicion for a blood clot or a local vein issue.
Idiopathic Edema in Younger Women
Some women experience recurring swelling in the feet, hands, and face without any identifiable heart, liver, or kidney disease. This condition, called idiopathic edema, occurs almost exclusively in premenopausal women and tends to follow a cyclical pattern, sometimes worsening before menstruation. The swelling can shift throughout the day, affecting the face in the morning and the feet by evening.
The exact cause isn’t well understood, and treatments are based on limited evidence. If you’re a younger woman dealing with unexplained, recurring foot swelling that doesn’t fit neatly into other categories, this diagnosis may come up after other conditions have been ruled out.