Leg swelling happens when fluid builds up in the tissues of your lower limb, and the cause ranges from something as simple as sitting too long to something that needs urgent medical attention. The single most important clue is whether one leg is swollen or both, because that distinction narrows the possibilities dramatically.
One Leg vs. Both: Why It Matters
Swelling in just one leg points toward a local problem: a blood clot, an infection, an injury, a blocked lymph vessel, or venous insufficiency on that side. Swelling in both legs usually signals something systemic, meaning a condition affecting your whole body, such as heart failure, kidney disease, a medication side effect, or chronic vein problems that have developed over years. There’s overlap between the two categories, but this one-or-both question is the first thing any clinician will assess, and it’s the most useful starting point for understanding what’s going on.
Blood Clots (DVT)
A deep vein thrombosis, or DVT, is a blood clot that forms in a deep vein, usually in the calf or thigh. It typically causes swelling in one leg along with pain or cramping that often starts in the calf, skin that turns red or purple, and a feeling of warmth in the affected area. Some DVTs produce no noticeable symptoms at all, which is part of what makes them dangerous. The clot can break loose and travel to the lungs, causing a pulmonary embolism.
DVT risk goes up after long periods of immobility (surgery recovery, a long flight, extended bed rest), with certain medications like hormonal birth control, during pregnancy, and in people with clotting disorders. If your leg swells suddenly on one side and feels warm or painful, that warrants same-day medical evaluation.
Venous Insufficiency
This is the single most common reason for chronic leg swelling. Somewhere between 10% and 35% of U.S. adults have chronic venous insufficiency, and the prevalence is higher in women and in people over 65. The underlying problem is that the one-way valves inside your veins stop working properly. Normally those valves keep blood flowing upward toward the heart. When they weaken or widen, blood flows backward and pools in the lower legs.
The pooling raises pressure inside the veins, which pushes fluid out into surrounding tissue. Over time this causes persistent swelling, aching, skin discoloration (often a brownish or reddish tone around the ankles), and in more advanced cases, open sores called venous ulcers. About 1% to 3% of adults eventually develop these ulcers, with the rate climbing to around 4% in people over 65. Previous DVT is one of the main triggers for venous insufficiency, because the clot damages the valves. But many people develop it without any known triggering event, simply from genetic predisposition, prolonged standing, obesity, or aging.
Lymphedema
Your lymphatic system drains excess fluid from tissues and returns it to the bloodstream. When lymph vessels are damaged or blocked, fluid accumulates and causes a distinctive type of swelling that feels firm and doesn’t indent easily when pressed. Lymphedema most commonly develops after cancer treatment that involves removing lymph nodes, but it can also be inherited or result from infection or injury.
One simple physical test helps identify it: try to pinch the skin on the top of your foot near the base of the toes. If the skin is too thick and swollen to pinch, that’s a positive Stemmer sign, which has about 92% sensitivity for lymphedema. A negative result is less conclusive, correctly ruling out the condition only about 57% of the time.
Heart, Kidney, and Liver Conditions
When the heart can’t pump blood efficiently, pressure builds in the veins, and fluid leaks into the tissues of both legs. Heart failure is one of the classic causes of bilateral leg swelling, often accompanied by shortness of breath, fatigue, and swelling that worsens over the course of the day. Kidney disease causes swelling through a different route: the kidneys fail to filter enough sodium and water, so blood volume rises and excess fluid gets pushed into tissues. Liver disease, particularly cirrhosis, reduces production of a protein called albumin that normally holds fluid inside blood vessels. When albumin drops, fluid seeps out more easily.
All three of these conditions tend to cause swelling in both legs symmetrically, and the swelling often extends to the feet and ankles. If you press a finger into the swollen area for several seconds and it leaves a visible dent that slowly fills back in, that’s called pitting edema, which is characteristic of these fluid-overload conditions.
Medications That Cause Swelling
Several common prescription drugs list leg swelling as a side effect. Blood pressure medications in the calcium channel blocker family are among the most frequent culprits. These drugs widen the small arteries feeding your tissues, which raises pressure inside the tiny capillaries and pushes fluid outward. The swelling is dose-dependent, meaning higher doses cause more of it.
Anti-inflammatory painkillers (both over-the-counter and prescription types) can also cause fluid retention. They reduce blood flow to the kidneys, which triggers the body to hold onto more sodium and water. Other medications linked to peripheral edema include certain diabetes drugs, steroids, some antidepressants and antipsychotics, and dopamine-related medications used for conditions like Parkinson’s disease. If your leg swelling started or worsened shortly after beginning a new medication, that timing is a strong clue.
Pregnancy-Related Swelling
Mild swelling in both legs during the third trimester is extremely common and usually harmless. The growing uterus compresses veins in the pelvis, slowing blood return from the legs, and pregnancy hormones make blood vessels more permeable to fluid. This type of swelling is typically worst at the end of the day and improves overnight.
What’s not normal is sudden, significant swelling, especially if it extends to the face or hands and comes with headaches or vision changes. Blood pressure at or above 140/90 mmHg combined with protein in the urine points toward preeclampsia, a serious pregnancy complication. Any rapid increase in swelling during pregnancy deserves prompt evaluation.
Sitting, Standing, and Travel
Even in perfectly healthy legs, gravity wins when you stay in one position too long. Sitting with your feet on the floor for hours causes blood to pool in the leg veins. The sustained pressure pushes fluid from the bloodstream into surrounding tissue, producing noticeable swelling in the feet and ankles. This is especially common during long flights because you’re sitting in a cramped position with limited movement, often for four or more hours straight.
People who stand all day at work experience the same thing through a slightly different mechanism: the calf muscles aren’t contracting and relaxing enough to pump blood upward. The result is occupational edema, temporary swelling that resolves once you lie down and elevate your legs.
Pitting Edema Grades
When a doctor presses a finger firmly into your swollen skin for about 20 seconds, they’re checking how deep the dent goes and how quickly it fills back in. The clinical grading scale runs from 1+ (a shallow indent of 2 to 4 millimeters) through 2+ (4 to 6 mm), 3+ (6 to 8 mm), and 4+ (deeper than 8 mm). Higher grades generally indicate more fluid accumulation and may prompt more aggressive investigation into the underlying cause. You can do a rough version of this test yourself to track whether your swelling is getting better or worse over time.
What You Can Do at Home
For swelling caused by prolonged sitting, standing, mild venous insufficiency, or travel, a few practical strategies help. Elevating your legs above heart level for 15 to 30 minutes several times a day lets gravity drain the excess fluid. Compression stockings apply graduated pressure that helps push fluid back into the veins. Stockings in the 15 to 20 mmHg range are effective for everyday occupational swelling, while 20 to 30 mmHg stockings provide stronger compression for people with established venous problems. Research shows both pressure ranges significantly reduce swelling compared to wearing no compression, with the 20 to 30 mmHg range performing slightly better.
Regular movement makes a meaningful difference. Walking, calf raises, or simply flexing your ankles while seated activates the calf muscle pump that pushes venous blood upward. Reducing salt intake helps if your swelling is related to fluid retention from heart, kidney, or medication issues. Maintaining a healthy weight reduces the pressure on your veins and lowers the overall risk of venous insufficiency progressing.
If your swelling is new, sudden, one-sided, painful, or accompanied by shortness of breath, chest pain, or skin that’s red and warm, those patterns suggest causes that need medical evaluation rather than home management.