Lower leg swelling happens when fluid leaks out of your blood vessels and gets trapped in the surrounding tissue. This is called edema, and it affects the legs more than anywhere else because gravity constantly pulls fluid downward. The causes range from something as simple as sitting too long to signs of a heart, kidney, or vein problem that needs attention.
How Fluid Ends Up Trapped in Your Legs
Your capillaries, the tiniest blood vessels in your body, are constantly filtering fluid outward into surrounding tissue. Blood pressure inside the capillary pushes fluid out, while proteins in your blood (mainly albumin) act like a sponge, pulling fluid back in. When these two forces are balanced, only a small amount of fluid escapes, and your lymphatic system drains what’s left over.
Swelling starts when something tips that balance. Higher pressure inside the veins pushes more fluid out. Lower protein levels in the blood reduce the “sponge” effect, so less fluid gets pulled back. A sluggish lymphatic system fails to drain the excess. Or some combination of all three. In the lower legs, gravity makes everything worse. Blood has to travel the longest distance back to your heart, and any time you’re sitting or standing still, fluid has extra time to accumulate.
Venous Insufficiency: The Most Common Culprit
The veins in your legs contain one-way valves that keep blood moving upward toward your heart. When those valves weaken or stop closing properly, blood pools in the lower legs. This raises the pressure inside the veins and forces fluid into the surrounding tissue. The condition is called chronic venous insufficiency, and it’s one of the most frequent reasons for persistent lower leg swelling.
You’ll typically notice the swelling gets worse as the day goes on and improves overnight when your legs are level with your heart. Over time, the skin on your lower legs may darken, feel tight, or become itchy. Varicose veins often accompany the problem. A duplex ultrasound can confirm the diagnosis by measuring blood flow direction in your leg veins.
Heart-Related Swelling
When the right side of your heart can’t pump blood efficiently to your lungs, blood backs up in the veins throughout your body. That backup raises pressure in the veins, pushing fluid into surrounding tissue. The result is swelling in the feet, ankles, and lower legs when you’re upright, or in the lower back if you’ve been lying down. Swelling in the abdomen can also develop as fluid accumulates around the liver and digestive organs.
Heart-related swelling tends to affect both legs equally and often comes alongside other symptoms: shortness of breath (especially when lying flat or during activity), fatigue, and a general feeling of heaviness. If your leg swelling appeared alongside breathing difficulty, that combination is worth prompt medical evaluation.
Kidney and Liver Disease
Your kidneys and liver both play roles in keeping albumin, the main protein in your blood, at adequate levels. Albumin is responsible for pulling fluid back into your bloodstream. When levels drop, fluid escapes more easily and stays in the tissue.
Kidney disease, specifically a condition called nephrotic syndrome, causes the kidneys to leak large amounts of protein into the urine. That protein loss lowers albumin in the blood, leading to swelling that often appears in the legs, around the eyes, and sometimes throughout the body. Liver disease causes a similar problem because the liver is where albumin is manufactured. When the liver is damaged, it can’t produce enough albumin to maintain that fluid-pulling effect.
Medications That Cause Leg Swelling
Certain blood pressure medications are well-known for causing ankle and lower leg swelling. Calcium channel blockers, a class of drugs commonly prescribed for high blood pressure, widen the small arteries, which increases pressure at the capillary level and pushes more fluid into tissue. At standard doses, anywhere from 1 to 15% of people taking these medications develop ankle swelling. At higher doses used long-term, that number can climb above 80%.
If you’re taking a calcium channel blocker and notice new leg swelling, it’s worth discussing with your prescriber. Adding a second type of blood pressure medication (one that works on a different system) can reduce swelling incidence significantly. One trial found that combining a calcium channel blocker with another class of blood pressure drug cut the rate of edema from about 19% to under 8%. Anti-inflammatory pain relievers, diabetes medications, and some hormone therapies can also contribute to fluid retention in the legs.
Blood Clots: When One Leg Swells Suddenly
A deep vein thrombosis, or DVT, is a blood clot that forms in a deep vein, usually in one leg. Unlike most other causes of leg swelling, DVT typically affects only one side. The swelling comes on relatively quickly and is often accompanied by pain or cramping in the calf, warmth in the affected leg, and skin that turns red or purple.
DVT becomes dangerous if the clot breaks loose and travels to the lungs, causing a pulmonary embolism. Warning signs of that complication include sudden shortness of breath, chest pain that worsens with deep breaths, a rapid pulse, dizziness, or coughing up blood. This is a medical emergency.
Lymphedema: A Different Kind of Swelling
Not all leg swelling involves fluid leaking from blood vessels. Lymphedema happens when your lymphatic system, the network of vessels responsible for draining excess fluid from tissue, is damaged or blocked. The fluid that builds up in lymphedema is thicker and protein-rich compared to the watery swelling of venous or heart-related edema.
One way to distinguish lymphedema from other types of swelling is the Stemmer sign. Try to pinch and lift the skin on the top of your foot near the base of your second toe. If the skin feels thick and you can’t lift it into a fold, that’s a positive Stemmer sign, which predicts lymphedema with about 88% sensitivity. Lymphedema also tends to feel firmer than typical edema, and pressing your finger into the swollen area may not leave a dent the way it does with other causes.
How to Check the Severity of Your Swelling
A simple way to gauge how significant your swelling is: press your thumb firmly into the swollen area for several seconds, then release. If it leaves an indentation, that’s called pitting edema. The deeper the dent and the longer it takes to fill back in, the more severe the swelling.
- 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 15 to 60 seconds to rebound.
- Grade 4: An 8 mm dent that persists for 2 to 3 minutes.
Grade 1 or 2 after a long day on your feet is common and often manageable at home. Grade 3 or 4, or swelling that doesn’t improve overnight, suggests something more is going on.
What Helps Reduce the Swelling
Elevating your legs above heart level is the simplest and most effective immediate measure. Lying on a couch with your feet propped on two pillows for 20 to 30 minutes allows gravity to work in your favor, helping fluid drain back toward your core.
Compression stockings apply graduated pressure to your legs, squeezing tightest at the ankle and gradually loosening up the calf. This helps push fluid upward and prevents it from pooling. For mild, occasional swelling, stockings rated at 15 to 20 mmHg provide light support. Most people with established swelling from venous insufficiency need 20 to 30 mmHg. More severe or persistent edema, particularly with skin changes or tissue firmness, often requires 30 to 40 mmHg. Getting the right fit matters, so it helps to have them sized when your legs are least swollen, usually in the morning.
Movement is equally important. Walking activates your calf muscles, which act as a pump to push blood upward through your veins. If your job keeps you sitting or standing in one position for hours, even brief walks or calf raises every 30 to 60 minutes can make a noticeable difference. Reducing your salt intake may help if your diet is particularly high in sodium, though the relationship between salt and fluid retention is more nuanced than commonly believed. People who already eat a moderate amount of salt may not see dramatic improvement from cutting back further, but those consuming large amounts of processed or restaurant food often do notice less swelling when they reduce sodium.
These measures manage the symptom. If your swelling is new, worsening, affecting only one leg, or accompanied by shortness of breath, skin changes, or pain, identifying the underlying cause is the more important step.