Swollen feet happen when fluid leaks out of tiny blood vessels and collects in the surrounding tissue, a condition called edema. This can be triggered by something as simple as standing too long or as serious as heart failure. Understanding the cause matters because some triggers resolve on their own while others need medical attention.
How Fluid Ends Up in Your Feet
Your smallest blood vessels, called capillaries, constantly exchange fluid with the tissue around them. Blood pressure inside these vessels pushes fluid outward, while proteins in your blood act like a sponge, pulling fluid back in. These two forces normally stay balanced. When something tips the balance, whether it’s higher pressure pushing fluid out or fewer proteins pulling it back, fluid accumulates in your tissues.
Gravity makes your feet the most common place for this to happen. Fluid naturally settles to the lowest point in your body, so even a minor imbalance in these forces shows up in your feet and ankles first. Your lymphatic system normally drains excess fluid from tissues and returns it to your bloodstream, but when fluid accumulates faster than the lymphatic system can handle, swelling develops.
Everyday Causes That Resolve on Their Own
Prolonged standing or sitting is the most common reason for swollen feet in otherwise healthy people. When your legs stay in one position for hours, gravity pulls blood downward and pressure builds in the veins of your lower legs. This forces more fluid into the surrounding tissue than usual. Long flights, desk jobs, and jobs that keep you on your feet all day are classic triggers.
Eating a high-sodium meal causes your body to retain water to keep your blood chemistry balanced, and that extra fluid often shows up in your feet. Heat is another trigger: warm temperatures cause blood vessels to widen, which increases fluid filtration into tissues. Pregnancy commonly causes foot swelling, especially in the third trimester, because of increased blood volume and pressure from the growing uterus on veins that return blood from the legs.
Chronic Venous Insufficiency
Your leg veins contain one-way valves that keep blood flowing upward toward your heart, fighting gravity with every step. Chronic venous insufficiency (CVI) happens when these valves become damaged and can no longer close properly. Blood flows backward, pools in the lower legs, and the increased pressure forces fluid into surrounding tissues. Over time, that sustained pressure can become severe enough to burst capillaries and cause skin changes or open sores called ulcers.
CVI is one of the most common causes of persistent foot and ankle swelling, particularly in people over 50. Risk factors include a history of blood clots, obesity, and spending long hours on your feet. The swelling typically worsens throughout the day and improves overnight when you’re lying flat. Compression stockings help by squeezing the veins and supporting the damaged valves, and staying active keeps the calf muscles pumping blood upward.
Heart, Kidney, and Liver Disease
Heart failure causes swollen feet through a straightforward chain of events. When the heart can’t pump blood efficiently, flow slows down and blood backs up in the veins returning from the legs. That backup raises pressure inside the blood vessels, and fluid leaks out into the tissues. Swelling in both feet that gets worse over the course of the day, combined with shortness of breath, is a hallmark pattern.
Kidney disease leads to swelling through a different path. When the kidneys can’t filter properly, sodium and water build up in the body. The extra fluid has to go somewhere, and gravity pulls it to the feet and ankles. Liver disease, particularly cirrhosis, reduces the liver’s ability to produce blood proteins. Since those proteins are what pulls fluid back into your blood vessels, lower protein levels mean more fluid stays trapped in tissues. A low-protein diet or malnutrition can cause the same effect.
Medications That Cause Swelling
Several common medications promote fluid retention as a side effect. Calcium channel blockers, a widely prescribed class of blood pressure drugs, are among the most frequent culprits. They relax blood vessel walls, which lowers blood pressure but also increases fluid leakage in the lower legs. Corticosteroids, certain diabetes medications, nonsteroidal anti-inflammatory drugs like ibuprofen, and some antidepressants can also cause noticeable foot swelling. Hormone therapies containing estrogen are another common trigger.
If your feet started swelling after beginning a new medication, that timing is worth noting. The swelling often resolves when the medication is adjusted, but never stop a prescribed drug without talking to your prescriber first.
Blood Clots: When One Foot Swells
A deep vein thrombosis (DVT) is a blood clot that forms in a deep vein, usually in the leg. Unlike most other causes of foot swelling, a DVT typically affects only one leg. Warning signs include swelling combined with pain or cramping (often starting in the calf), skin that feels warm to the touch, and a change in skin color to red or purple. This is a medical emergency because the clot can break free and travel to the lungs, a life-threatening condition called a pulmonary embolism.
Risk factors for DVT include recent surgery, long periods of immobility (including long flights or bed rest), cancer, and a personal or family history of blood clots. If one foot or leg suddenly swells and feels painful or warm, seek medical care immediately rather than waiting to see if it resolves.
Infections and Lymphatic Problems
Cellulitis, a bacterial skin infection, causes localized swelling along with warmth, pain, redness, and sometimes fever or chills. The infection triggers inflammation that increases fluid leakage from blood vessels in the affected area. What makes this a two-way problem is that chronic swelling itself raises the risk of cellulitis. Bacteria are more likely to enter skin that’s already swollen, stretched, cracked, or broken. People with long-term edema in their legs are especially vulnerable, and repeated cellulitis episodes can damage lymph nodes, creating a cycle where each infection makes future swelling worse.
Lymphedema, a condition where the lymphatic drainage system is blocked or damaged, causes persistent swelling that doesn’t respond to elevation the way other types of edema do. It can develop after surgery that removes lymph nodes, after radiation therapy, or from chronic infections. The swelling tends to feel firmer than fluid-related edema and may affect one leg more than the other.
How to Tell If Swelling Is Mild or Serious
A simple way to gauge the severity of swelling is the pitting test. Press your thumb firmly into the swollen area near your shin for a few seconds, then release. If the skin bounces back immediately and no dent remains, the swelling is minimal. If a visible dent lingers, that’s called pitting edema, and the deeper the dent and the longer it takes to refill, the more fluid has accumulated. Clinicians use a 0 to 4+ scale: at the low end, pitting is slight and stays below the knee; at the high end, the dent is deep, slow to rebound, and the swelling extends above the knee.
Swelling in both feet that comes and goes with activity and improves overnight is usually less concerning than swelling that’s persistent, worsening, or accompanied by other symptoms. Red flags that point to something more serious include swelling in only one leg (suggesting a clot), shortness of breath alongside bilateral swelling (suggesting a heart or lung problem), decreased urine output (suggesting kidney issues), and signs of infection like redness, warmth, and fever.