Leg swelling happens when fluid leaks out of tiny blood vessels and collects in the surrounding tissue. This can be triggered by something as simple as sitting too long or as serious as heart failure. The underlying cause determines whether swelling is harmless and temporary or a sign that something needs medical attention.
Your body constantly moves fluid between your bloodstream and surrounding tissues. This exchange is governed by pressure inside blood vessels pushing fluid out and proteins in your blood pulling fluid back in. When that balance tips, fluid accumulates in the tissue, and gravity pulls it down to your legs, ankles, and feet.
The Most Common Everyday Causes
Prolonged sitting or standing is the simplest explanation for swollen legs. When your calf muscles aren’t contracting, they can’t pump blood back up toward your heart. Pressure builds in the veins of your lower legs, and fluid seeps into the surrounding tissue. Long flights, desk jobs, and extended periods on your feet all create this effect. Moving around, elevating your legs, or flexing your calves periodically is usually enough to resolve it.
High salt intake plays a direct role. Sodium causes your body to retain water, increasing the volume of fluid in your bloodstream and raising the pressure that pushes fluid out of your capillaries. Hot weather compounds the problem because your blood vessels dilate in the heat, which further increases pressure in the veins of your lower legs. Many people notice their ankles swell more in summer for exactly this reason.
Vein Problems and Chronic Venous Insufficiency
Your leg veins contain one-way valves that keep blood flowing upward against gravity. When those valves weaken or fail, blood pools in the lower legs, a condition called chronic venous insufficiency. This is one of the most common causes of persistent leg swelling, particularly in people over 50.
Valve failure can happen in the superficial veins near the skin’s surface, the deep veins surrounded by muscle, or the perforator veins that connect the two systems. In superficial veins, the problem often starts with a pre-existing weakness in the vessel wall or valve leaflets. Deep vein valve damage is most often a consequence of a previous blood clot. When perforator valves fail, the high pressures generated by your calf muscles force blood backward into the superficial veins, stretching them out and causing their valves to fail in a cascade effect.
Weak calf muscles make the situation worse. Your calf muscles act as a pump, squeezing blood upward with each step. If that pump isn’t working effectively, whether due to inactivity, muscle weakness, or nerve damage, your veins can’t empty properly. Over time, chronic venous insufficiency can cause skin darkening around the ankles, visible varicose veins, and in severe cases, open sores on the lower legs.
Heart, Kidney, and Liver Disease
When the heart can’t pump blood efficiently, pressure backs up in the veins, forcing fluid into the tissues. Heart failure typically causes swelling in both legs, ankles, and feet, and it tends to worsen over the course of the day and improve overnight when you’re lying flat. You might also notice shortness of breath, fatigue, or swelling in the abdomen.
Kidney disease causes swelling through a different path. When your kidneys can’t filter and remove fluid effectively, your total blood volume increases. The two conditions are closely linked: people with chronic kidney disease have a higher risk of heart failure, and both conditions share fluid overload as a central problem. Reducing salt intake and managing fluid balance are cornerstones of treatment for both.
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 more easily. Severe malnutrition can produce the same effect. This type of swelling often affects the abdomen as well as the legs.
Medications That Cause Swelling
Several widely prescribed medications list leg swelling as a side effect. Calcium channel blockers, a class of blood pressure medications, are among the most common culprits. At standard doses, somewhere between 1% and 15% of people on these drugs develop ankle swelling. At higher doses taken long-term, that number can exceed 80%. The swelling is dose-related, so it often appears or worsens when the dose is increased.
Combining a calcium channel blocker with certain other blood pressure medications can reduce swelling significantly. In one clinical trial, patients taking amlodipine combined with another blood pressure drug had an edema rate of 7.6%, compared to 18.7% in those taking amlodipine alone. Other medications that commonly cause leg swelling include corticosteroids, some diabetes drugs, nonsteroidal anti-inflammatory drugs like ibuprofen, and certain antidepressants. If you notice new swelling after starting a medication, your prescriber can often adjust the dose or switch to an alternative.
Blood Clots: The Warning to Watch For
A deep vein thrombosis (DVT) is a blood clot that forms in a deep vein, usually in the leg. Unlike most other causes of swelling, a DVT almost always affects just one leg. The swollen leg may feel warm, look reddish or discolored, and hurt, especially in the calf when you flex your foot upward. A difference of 3 centimeters or more in calf circumference between your two legs, measured about 10 centimeters below the knee, is a clinical marker that raises suspicion for a clot.
DVTs are dangerous because a piece of the clot can break loose and travel to the lungs, causing a pulmonary embolism. Risk factors include recent surgery, long periods of immobility, cancer, pregnancy, and a personal or family history of clots. If you develop sudden, unexplained swelling in one leg with pain or warmth, seek medical attention promptly. Ultrasound is the standard test for diagnosing DVT, with a detection rate above 96% for clots in the thigh and upper leg.
Pregnancy-Related Swelling
Some degree of leg and ankle swelling is normal during pregnancy, especially in the third trimester. The growing uterus puts pressure on the veins that return blood from the legs, and hormonal changes cause the blood vessel walls to relax. Mild, symmetrical swelling that comes and goes is generally not a concern.
Sudden or severe swelling, however, can signal preeclampsia, a serious pregnancy complication. Preeclampsia is diagnosed when blood pressure reaches 140/90 mmHg or higher along with signs of organ stress, such as protein in the urine. Severe preeclampsia involves blood pressure at or above 160/110 mmHg. Swelling alone doesn’t confirm preeclampsia, but rapid onset of swelling in the face, hands, or legs, combined with headaches, vision changes, or upper abdominal pain, warrants immediate evaluation.
How to Assess Your Swelling
A simple way to gauge the severity of swelling is the pitting test. Press a fingertip firmly into the swollen area for several seconds, then release. If your finger leaves an indentation, the swelling is “pitting edema,” and the depth and recovery time tell you how severe it is:
- Grade 1: A 2 mm dent that rebounds immediately. Mild.
- 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 takes two to three minutes to fill. Severe.
Grade 1 swelling that appears after a long day and resolves with leg elevation is usually nothing to worry about. Grade 3 or 4, swelling that persists day after day, or swelling accompanied by shortness of breath, chest pain, or skin changes points to something that needs investigation.
Managing Mild to Moderate Swelling
For swelling related to vein problems, prolonged sitting, or mild fluid retention, compression stockings are one of the most effective tools. They work by applying graduated pressure, strongest at the ankle and decreasing up the leg, to help push fluid back into circulation. Stockings rated at 20 to 30 mmHg (moderate compression) are appropriate for most people with everyday swelling or early venous insufficiency. Stronger stockings in the 30 to 40 mmHg range are used for more significant venous disease or after a blood clot.
Elevating your legs above heart level for 15 to 30 minutes several times a day helps fluid drain back toward your core. Regular walking strengthens the calf muscle pump. Cutting back on sodium reduces fluid retention. These measures work well for mechanical and lifestyle-related swelling, but they won’t resolve swelling caused by an underlying organ problem. Persistent or worsening swelling, particularly if it’s new, one-sided, or accompanied by other symptoms, is worth getting checked out to identify whether a deeper cause is at play.