Swollen legs happen when fluid leaks from tiny blood vessels and collects in the surrounding tissue. This is called edema, and it affects roughly 20% of adults over age 50. The causes range from sitting too long on a flight to serious conditions like heart failure or blood clots, so the key is figuring out whether your swelling is in one leg or both, and whether it came on suddenly or built up over time.
One Leg vs. Both Legs
This distinction matters more than almost anything else when sorting out the cause. Swelling in just one leg raises concern for a blood clot (deep vein thrombosis), infection, injury, or a ruptured cyst behind the knee. Swelling in both legs points toward something systemic: heart problems, kidney or liver disease, medication side effects, or chronic vein issues. Both legs swelling at the same time usually means fluid is building up throughout your body and gravity is pulling it downward.
Common Causes of Swelling in Both Legs
Heart Failure
When the heart can’t pump blood efficiently, blood backs up in the veins of your legs, ankles, and feet. The increased pressure forces fluid out of the blood vessels and into surrounding tissue. You might also notice that your shoes feel tighter in the evening, that you gain weight quickly over a few days, or that you get short of breath when lying flat. These are all signs the heart is struggling to keep up.
Kidney and Liver Disease
Your blood contains a protein called albumin that acts like a sponge, keeping fluid inside your blood vessels. Kidney disease (particularly nephrotic syndrome) causes albumin to spill into the urine, while liver disease like cirrhosis reduces albumin production. Either way, the result is the same: without enough albumin, fluid seeps out of the bloodstream and pools in your legs and sometimes your abdomen.
Chronic Venous Insufficiency
This is one of the most common causes of persistent leg swelling. The veins in your legs have one-way valves that push blood back up toward the heart. When those valves weaken or fail, blood pools in the lower legs. The swelling tends to worsen throughout the day, improve overnight, and get worse in hot weather. You may also notice skin discoloration, varicose veins, or a heavy, achy feeling.
Medications
A surprising number of medications can cause leg swelling as a side effect. Blood pressure drugs like amlodipine and nifedipine are among the most common culprits. They relax blood vessel walls in a way that increases pressure inside the smallest vessels, pushing fluid out. Anti-inflammatory drugs (ibuprofen, naproxen, corticosteroids), nerve pain medications like gabapentin and pregabalin, hormone therapies (estrogen, testosterone, progesterone), and certain diabetes medications can all do the same. If your swelling started shortly after beginning a new prescription, that connection is worth investigating.
Pregnancy and Hormonal Changes
Pregnancy causes the body to retain extra fluid and increases pressure on the veins returning blood from the legs. Some degree of leg swelling is normal during pregnancy, especially in the third trimester. Hormonal fluctuations outside of pregnancy, including those related to the menstrual cycle, can also cause mild fluid retention.
Prolonged Sitting or Standing
Gravity works against you when you stay in one position for hours. Sitting at a desk all day, taking a long flight, or standing for a full shift can cause fluid to accumulate in your lower legs simply because there’s no muscle movement to pump it back up. This type of swelling is usually mild, affects both legs equally, and resolves once you move around or elevate your feet.
When Swelling Is in One Leg
Single-leg swelling that appears suddenly deserves prompt attention. Deep vein thrombosis, a blood clot in a deep leg vein, is the most concerning possibility. Signs include swelling in one leg along with pain or cramping that often starts in the calf, skin that looks red or purple, and warmth in the affected leg. A clot can break loose and travel to the lungs, causing a pulmonary embolism. Warning signs of that include sudden shortness of breath, chest pain that worsens when you breathe deeply, dizziness, a rapid pulse, or coughing up blood. Those symptoms require emergency care.
Other causes of one-sided swelling include infections (especially if the skin is red, hot, and tender), injuries like muscle tears or fractures, and lymphedema, where the lymphatic drainage system is blocked or damaged. Lymphedema often develops gradually and causes a firm, non-pitting swelling that doesn’t indent easily when you press on it.
Pitting vs. Non-Pitting Edema
If you press a finger into the swollen area for a few seconds and it leaves an indentation, that’s pitting edema. Healthcare providers grade it on a scale of 1 to 4 based on how deep the pit is and how long it takes to bounce back. A grade 1 pit is about 2 millimeters deep and rebounds immediately. A grade 4 pit is about 8 millimeters deep and takes two to three minutes to fill back in. Higher grades indicate more fluid buildup. Pitting edema is typical of heart, kidney, liver, and vein-related causes.
Non-pitting edema, where the skin springs back right away without leaving a dent, is more characteristic of thyroid disease or lymphedema. The distinction helps narrow down the underlying cause.
What You Can Do at Home
For mild swelling without other worrying symptoms, a few strategies can help move fluid out of your legs. Elevate your legs above the level of your heart for about 15 minutes, three to four times a day. This lets gravity work in your favor instead of against you. Lying on a couch or bed with your legs propped on pillows works well.
Movement is equally important. Walking, flexing your ankles, or doing simple calf raises activates the muscle pump in your lower legs that pushes blood and fluid upward. If your job keeps you sitting or standing for long stretches, take breaks every 30 to 60 minutes to change position.
Reducing salt intake helps limit fluid retention. For people prone to edema, keeping daily sodium between 1,375 and 1,800 milligrams is a common target. For perspective, a single fast-food meal can exceed that in one sitting. Reading nutrition labels, cooking at home more often, and cutting back on processed foods are the most practical ways to lower your intake.
Compression stockings apply graduated pressure to your legs, with the tightest squeeze at the ankle, to help push fluid upward. They come in different pressure levels, from light support (18 to 21 mmHg) for mild swelling up to medical-grade options (34 mmHg and higher) for more severe cases. The right level depends on your condition and physical ability, so it’s worth getting a recommendation rather than guessing.
Signs That Need Urgent Attention
Leg swelling paired with chest pain, difficulty breathing, shortness of breath when lying down, dizziness, or coughing up blood may signal a blood clot in the lungs or a serious heart problem. These combinations require emergency care. You should also seek prompt evaluation if your swelling appears suddenly for no clear reason, follows a physical injury, or involves only one leg with pain, coolness, or color changes in the skin.
Swelling that gets progressively worse over weeks, causes skin changes like thickening or discoloration, or comes with unexplained weight gain also warrants a medical evaluation. Identifying the root cause is what makes the difference between managing the symptom and actually fixing the problem.