Swelling in the feet and ankles happens when fluid leaks out of small blood vessels and accumulates in surrounding tissues faster than your body can drain it away. The most common cause is simply gravity: standing or sitting for long periods pulls blood downward, and water seeps from veins into the tissue of your legs and feet. But persistent or sudden swelling can also signal problems with your veins, heart, kidneys, or liver, or be a side effect of medication.
Gravity, Inactivity, and Everyday Swelling
Your veins have tiny one-way valves designed to keep blood moving upward against gravity. When you stand or sit still for hours, your calf muscles aren’t contracting to push blood back toward your heart. Gravity wins, blood pools in the leg veins, and water from that blood crosses into surrounding tissues. This is why your feet may feel tight in your shoes at the end of a long day or after a flight.
This type of swelling is usually mild, affects both feet equally, and goes down overnight or when you elevate your legs. It’s more common in hot weather (heat dilates blood vessels, making them leakier), during pregnancy, and in people who carry extra weight. On its own, it isn’t dangerous. But if swelling persists even after rest and elevation, something else is likely going on.
Chronic Venous Insufficiency
Chronic venous insufficiency is the most common medical cause of ongoing swelling in both legs. It develops when the valves inside your leg veins stop closing properly. Instead of flowing upward toward the heart, blood falls backward and pools, creating sustained high pressure in the veins of your lower legs. That pressure pushes fluid, proteins, and even red blood cells through the walls of tiny capillaries into the tissue around your ankles and feet.
Over time, the leaked red blood cells break down and leave brownish discoloration on the skin, especially around the inner ankle. Skin can become thick, hard, and itchy. In advanced cases, open sores (venous ulcers) can develop near the ankle. Varicose veins, a history of blood clots, obesity, and jobs that require prolonged standing all raise the risk. If you notice skin color changes along with swelling, venous insufficiency is a likely culprit.
Heart Failure
When the heart can’t pump blood efficiently, pressure builds in the veins. The body also responds to falling blood pressure by activating hormonal systems that tell the kidneys to hold onto salt and water. The result is an absolute excess of fluid in the body. Because gravity pulls hardest at the lowest point, that extra fluid shows up first in the feet and ankles.
Heart failure-related swelling tends to worsen throughout the day and improve overnight. It typically affects both legs. Other signs include shortness of breath (especially when lying flat), fatigue, a swollen abdomen, and waking up at night gasping for air. If your ankle swelling comes with any of these symptoms, it points toward a cardiac cause rather than a vein problem.
Kidney and Liver Disease
Your blood needs a certain concentration of protein, particularly albumin, to hold fluid inside the blood vessels. Albumin is responsible for 75 to 80% of the pulling force that keeps water from leaking out of capillaries. When the kidneys spill large amounts of protein into the urine, or the liver fails to produce enough albumin, that pulling force drops and fluid seeps into tissues throughout the body, including the feet and ankles.
Kidney disease can also impair your body’s ability to excrete salt and water, compounding the problem. Liver disease, especially cirrhosis, often causes swelling in both the legs and the abdomen. These conditions usually produce swelling that’s bilateral and persistent, and they’re often accompanied by other symptoms like fatigue, changes in urination, or abdominal bloating.
Blood Clots
A deep vein thrombosis (DVT) is a blood clot that forms in one of the deep veins of the leg. It partially or fully blocks blood flow, causing a backup of pressure and fluid. The hallmark of DVT is swelling that appears in one leg only, often with pain, warmth, and redness in the calf or thigh.
This distinction matters. Swelling in both feet usually points to a systemic cause like vein disease, heart failure, or medication. Sudden swelling in just one leg is a red flag for DVT and needs prompt evaluation, typically with an ultrasound. A clot can break free and travel to the lungs, causing a pulmonary embolism. Warning signs of that complication include sudden shortness of breath, sharp chest pain that worsens with breathing, a rapid heartbeat, coughing up blood, and pale or bluish skin. Those symptoms require emergency care.
Lymphedema
Your lymphatic system acts as a secondary drainage network, collecting excess fluid from tissues and returning it to the bloodstream. When lymph vessels are damaged or blocked, fluid accumulates and produces a distinctive, firm type of swelling that doesn’t pit easily when you press it.
Lymphedema can be inherited (primary) or develop after surgery, radiation therapy, infection, or severe chronic vein disease. Damaged veins can overwhelm the lymphatic system over time: the extra fluid overflowing from leaky veins eventually exhausts the lymph vessels’ capacity to drain it. Lymphedema tends to progress gradually, starting at the foot or toes and working upward. Unlike venous edema, it often doesn’t improve much with elevation alone.
Medications That Cause Swelling
Several commonly prescribed drugs can cause fluid to accumulate in the ankles. The most well-known culprits are calcium channel blockers, a class of blood pressure medications. These drugs relax artery walls but don’t have the same effect on veins, so more blood flows into the legs than can easily flow back out. At standard doses, ankle swelling affects roughly 1 to 15% of patients. At higher doses taken long-term, the incidence can exceed 80%.
Adding a second type of blood pressure medication that acts on the body’s salt-retention hormones can reduce swelling by about 38% compared to taking a calcium channel blocker alone. Other medications linked to ankle edema include certain diabetes drugs, anti-inflammatory painkillers (NSAIDs), steroids, and some hormone therapies. If your swelling started shortly after beginning a new medication, that connection is worth raising with your prescriber.
Pregnancy-Related Swelling
Some degree of foot and ankle swelling is normal during pregnancy, especially in the third trimester. The growing uterus compresses pelvic veins, slowing blood return from the legs, and the body naturally retains more fluid to support the pregnancy.
What’s not normal is sudden swelling, particularly in the face and hands, accompanied by headaches, vision changes, or upper abdominal pain. These can be signs of preeclampsia, a serious blood pressure condition that develops after 20 weeks of pregnancy. Gradual, symmetrical ankle puffiness that eases with rest is expected. A rapid change deserves prompt medical evaluation.
How Doctors Assess the Severity
When you press a swollen ankle with your finger and it leaves a dent, that’s called pitting edema. Doctors grade it on a 1 to 4 scale based on how deep the dent is and how long it takes to bounce back:
- Grade 1: A shallow 2 mm dent that rebounds immediately.
- Grade 2: A 3 to 4 mm dent that fills back in within 15 seconds.
- Grade 3: A 5 to 6 mm dent that takes up to 60 seconds to rebound.
- Grade 4: An 8 mm dent that can take two to three minutes to fill back in.
Higher grades suggest more fluid accumulation and often point toward a systemic cause like heart, kidney, or liver problems rather than a local vein issue. If swelling doesn’t pit at all and feels firm or spongy, lymphedema is more likely.
One Leg vs. Both Legs
The pattern of swelling is one of the most useful clues to its cause. Swelling in both feet and ankles that develops gradually points toward chronic venous insufficiency, heart failure, kidney or liver disease, medication effects, or prolonged inactivity. Sudden swelling in one leg raises concern for a blood clot or, less commonly, a local infection or injury. Chronic swelling in one leg that starts at the toes and slowly worsens suggests lymphedema, possibly from prior surgery, radiation, or an underlying vein problem that has overwhelmed the lymphatic system.
Paying attention to when the swelling appears, whether it’s worse at certain times of day, whether it affects one side or both, and whether it comes with other symptoms like breathlessness, skin changes, or pain gives you and your doctor the most useful starting information for figuring out the cause.