Feet swell when excess fluid builds up in the tissues of the lower legs and feet, a condition called peripheral edema. The causes range from something as simple as sitting too long on a flight to serious conditions like heart failure or a blood clot. Understanding the pattern of your swelling, whether it affects one foot or both, and how quickly it appeared can help narrow down what’s behind it.
How Fluid Ends Up in Your Feet
Gravity plays a constant role. Blood circulates down to your feet easily, but returning it upward to your heart requires working leg muscles and functioning valves inside your veins. Anything that disrupts this return flow, increases pressure in your blood vessels, or causes your body to hold onto extra salt and water can push fluid out of your bloodstream and into the surrounding tissue. That fluid pools in your feet and ankles first because they’re the lowest point of your body.
When you press on swollen skin and it leaves a temporary dent, that’s called pitting edema. Doctors grade it on a scale from 1 to 4 based on how deep the dent is and how long it takes to bounce back. A grade 1 pit is about 2 millimeters deep and rebounds immediately. A grade 4 pit is 8 millimeters deep and can take two to three minutes to fill back in. The grade helps indicate how much fluid has accumulated.
Standing, Sitting, and Heat
The most common cause of swollen feet is simply being on them all day, or paradoxically, sitting still for hours. When your calf muscles aren’t contracting, they can’t pump blood back up toward your heart. Long flights, desk jobs, and road trips are classic triggers. Hot weather makes it worse because your blood vessels widen to release heat, which allows more fluid to seep into surrounding tissue. This type of swelling is usually mild, affects both feet equally, and goes down overnight when you lie flat.
Too Much Salt in Your Diet
Your body tightly regulates the balance between sodium and water. When you eat a salty meal, your kidneys hold onto extra water to dilute the sodium, increasing your overall fluid volume. The American Heart Association recommends staying under 2,300 milligrams of sodium per day, but the average American consumes well over that. If you’re salt-sensitive, meaning your body reacts more strongly to sodium intake, even moderate amounts can noticeably raise your blood pressure and cause fluid retention in your feet and ankles. Processed foods, restaurant meals, and canned soups are common culprits.
Medications That Cause Swelling
Several widely prescribed drug classes cause feet to swell as a side effect, and many people don’t realize their medication is the reason.
Blood pressure medications in the calcium channel blocker family are among the most common offenders. Between 1% and 15% of people taking these drugs develop ankle swelling at standard doses. At higher doses used long-term, the incidence can exceed 80%. The swelling happens because these drugs relax blood vessel walls, which lowers blood pressure but also lets more fluid leak into tissue.
Common pain relievers like ibuprofen and naproxen cause visible edema in 3% to 5% of users. These drugs reduce your kidneys’ ability to flush out sodium and water by roughly 30%, leading to fluid buildup. Corticosteroids (often prescribed for inflammation or autoimmune conditions) cause edema in about 20% of users, with the risk climbing at higher doses taken for more than a year. Hormonal medications, including oral contraceptives, trigger sodium and fluid retention in about 5% of users by activating a hormonal cascade that tells the kidneys to hold onto water.
If your feet started swelling after beginning a new medication, that timing is worth noting. The swelling often resolves when the drug is adjusted, but never stop a prescribed medication without guidance.
Heart Failure
When the heart can’t pump blood efficiently, a chain reaction begins. Blood backs up in the veins, pressure builds, and fluid gets forced out into surrounding tissues. This is one of the hallmark signs of congestive heart failure. The swelling typically affects both legs and feet, worsens throughout the day, and may be accompanied by shortness of breath, fatigue, or a persistent cough. In heart failure, the kidneys also receive less blood flow and respond by retaining even more salt and water, compounding the problem.
Heart-related swelling tends to develop gradually over weeks and progressively worsen. It often leaves deep pitting marks when you press on the skin. If you notice your shoes getting tighter over time, unexplained weight gain of several pounds over a few days, or difficulty breathing when lying flat, these are patterns worth taking seriously.
Vein Problems in the Legs
Chronic venous insufficiency occurs when the one-way valves inside your leg veins stop working properly. Instead of pushing blood upward toward the heart, damaged valves let blood fall backward and pool in the lower legs. Over time, the sustained pressure forces fluid into the surrounding tissue.
This condition develops gradually and has a recognizable progression. Early signs include legs that feel heavy, achy, or fatigued by the end of the day, along with ankle swelling that improves overnight. As it advances, the skin around the ankles may darken to a brownish color, become dry and itchy, or develop a leathery texture. Visible spider veins or bulging varicose veins are common. In severe cases, the skin can break down into slow-healing ulcers near the ankle. The swelling from venous insufficiency can affect one leg more than the other, which helps distinguish it from other causes.
Blood Clots: When One Foot Swells Suddenly
A deep vein thrombosis (DVT) is a blood clot that forms in a deep vein, usually in the leg. It typically causes sudden swelling in just one leg, along with pain or cramping that often starts in the calf, warmth in the affected area, and skin that turns red or purple. This is a medical emergency because the clot can break loose and travel to the lungs, causing a pulmonary embolism.
Warning signs that a clot has reached the lungs include sudden shortness of breath, chest pain that worsens when you breathe deeply or cough, a rapid pulse, dizziness or fainting, and coughing up blood. These symptoms require immediate emergency care. Risk factors for DVT include recent surgery, prolonged immobility (like a long hospital stay or flight), cancer, pregnancy, and a personal or family history of clotting disorders.
Pregnancy-Related Swelling
Some degree of foot and ankle swelling is normal during pregnancy, especially in the third trimester. The growing uterus puts pressure on veins that return blood from the legs, and hormonal changes cause the body to retain more fluid overall. This swelling is usually mild, affects both feet, and worsens in hot weather or after standing.
Swelling becomes concerning when it appears suddenly in the hands and face, not just the feet. This pattern can signal preeclampsia, a serious pregnancy complication diagnosed by high blood pressure (140/90 mmHg or above) and protein in the urine after 20 weeks of gestation. Preeclampsia affects both the mother and baby and requires medical management. Sudden, severe swelling during pregnancy, particularly above the ankles, warrants prompt evaluation.
Kidney and Liver Disease
Your kidneys filter excess fluid and sodium from your blood. When they’re not functioning well, that fluid accumulates in your body, often settling in the feet, ankles, and around the eyes. Kidney-related swelling tends to affect both sides equally and may be accompanied by changes in urination, foamy urine, or persistent fatigue.
Liver disease, particularly cirrhosis, reduces your liver’s ability to produce albumin, a protein that keeps fluid inside your blood vessels. When albumin levels drop, fluid leaks out into tissues. Liver-related swelling often appears alongside abdominal bloating from fluid accumulation in the belly.
Reducing and Managing Swelling
For mild, everyday swelling caused by gravity, heat, or diet, a few practical strategies make a real difference. Elevating your feet above heart level for 20 to 30 minutes helps fluid drain back toward your core. Moving your calf muscles regularly, even just flexing your ankles up and down while sitting, activates the muscle pump that pushes blood upward. Cutting back on sodium gives your kidneys less reason to retain water.
Compression stockings apply graduated pressure that supports your veins and prevents fluid from pooling. For mild swelling or prevention, stockings in the 15 to 20 mmHg range provide light support. More significant swelling from venous insufficiency typically calls for 20 to 30 mmHg or higher, while severe cases with tissue changes may require 40 to 50 mmHg under clinical guidance.
Swelling that appears suddenly in one leg, doesn’t improve with elevation, gets progressively worse over weeks, or comes with shortness of breath, chest pain, or significant skin changes points to something beyond a long day on your feet. The pattern matters: both feet swelling gradually suggests a systemic cause like heart, kidney, or medication issues, while one leg swelling suddenly raises concern for a blood clot or localized vein problem.