Leg swelling happens when fluid builds up in the tissues of your lower extremities, and the list of possible causes ranges from eating too much salt to serious conditions like heart failure or blood clots. Whether one leg or both legs are swollen is one of the most important clues to what’s going on, because the underlying causes are often very different.
One Leg vs. Both Legs: Why It Matters
Swelling in just one leg typically points to a local problem: a blood clot, an injury, an infection, or a vein that isn’t working properly. Swelling in both legs usually signals something systemic, meaning a condition affecting your whole body, like heart failure, kidney disease, or liver problems. There are exceptions. Chronic vein disease and lymphatic damage can affect both legs, but they tend to be uneven, with one side worse than the other. And sometimes a person with a systemic cause develops a separate local problem on top of it, making one leg noticeably more swollen.
Blood Clots in the Deep Veins
A deep vein thrombosis (DVT) is a blood clot that forms in one of the large veins deep inside the leg. It’s one of the more urgent causes of sudden, one-sided leg swelling. Along with swelling, you may notice pain or cramping that often starts in the calf, warmth in the affected leg, and skin that turns red or purple. Some DVTs cause no noticeable symptoms at all, which is part of what makes them dangerous.
The real emergency isn’t the clot itself but what happens if a piece breaks off and travels to the lungs, causing a pulmonary embolism. Warning signs of that include sudden shortness of breath, chest pain that gets worse when you breathe deeply or cough, a rapid pulse, dizziness or fainting, and coughing up blood. Any combination of these symptoms warrants a call to emergency services.
Chronic Venous Insufficiency
Your leg veins contain one-way valves that push blood upward toward your heart, fighting gravity with every step. When those valves become damaged, blood flows backward and pools in the lower legs, a condition called chronic venous insufficiency (CVI). The increased pressure in your veins forces fluid out into surrounding tissue, causing swelling that’s usually worst after standing for a long time or by the end of the day.
Over time, untreated CVI raises the pressure in your leg veins so much that the tiniest blood vessels can burst. This can lead to skin discoloration, thickening, and eventually open sores (venous ulcers) near the ankles. CVI is one of the most common causes of persistent leg swelling and tends to get progressively worse without management.
Heart, Kidney, and Liver Disease
When the heart can’t pump blood efficiently, as in congestive heart failure, blood backs up in the veins. That backup raises pressure inside the capillaries and pushes fluid into the tissues, especially in the legs and ankles where gravity pulls it. At the same time, reduced blood flow to the kidneys triggers a cascade of hormonal signals that tell the body to hold on to salt and water, making the swelling even worse. The kidneys themselves are structurally normal in heart failure, but they keep retaining fluid because the body’s volume-sensing systems are essentially being tricked by poor circulation.
Kidney disease causes swelling through a more direct route: the kidneys simply can’t filter and excrete enough fluid. Liver disease, particularly cirrhosis, leads to low levels of a protein called albumin in the blood. Albumin acts like a sponge that keeps fluid inside blood vessels. When levels drop, fluid leaks out into tissues. All three of these conditions tend to cause swelling in both legs, and often the swelling extends to the abdomen, hands, or face as well.
Lymphedema
Your lymphatic system is a network of vessels that drains excess fluid from tissues and returns it to the bloodstream. When those vessels are blocked or damaged, fluid accumulates and the affected limb swells. Cancer treatment is the most common cause in developed countries, particularly surgery or radiation that removes or damages lymph nodes. Cancer itself can cause lymphedema if a tumor grows large enough to block lymph drainage. In tropical regions, parasitic infections that clog lymph nodes are the leading cause.
Lymphedema feels different from other types of swelling. The affected area often feels heavy and tight rather than soft and squishy. Over time, the skin can harden and thicken. The swelling may start in the fingers or toes and spread, and it doesn’t resolve as easily with elevation. Some people are born with lymphatic systems that didn’t develop properly, leading to lymphedema that appears in childhood or early adulthood without any obvious trigger.
Medications That Cause Swelling
A surprisingly long list of common medications can trigger leg swelling as a side effect. The most frequent culprits are calcium channel blockers, a class of blood pressure drugs that includes amlodipine, nifedipine, and felodipine. These medications relax blood vessel walls, which can allow more fluid to leak into surrounding tissues. Hormone-related medications are another major category: testosterone, estrogen, progesterone, and corticosteroids all promote fluid retention.
Other medications linked to leg swelling include certain diabetes drugs (particularly the thiazolidinedione class), some antidepressants, NSAIDs like ibuprofen and naproxen, and even proton pump inhibitors used for acid reflux. If your legs started swelling after beginning a new medication, that connection is worth raising with whoever prescribed it.
Salt, Gravity, and Everyday Causes
Not all leg swelling signals a medical condition. High salt intake is one of the most straightforward triggers. A study of elderly men found that daily salt consumption directly correlated with the amount of fluid that accumulated in the legs by late afternoon. The mechanism is simple: sodium pulls water into your blood vessels, increasing overall fluid volume, and gravity draws that extra fluid downward throughout the day.
Prolonged sitting or standing has the same gravitational effect. Long flights, desk jobs, and any position where your legs hang down for hours can produce noticeable ankle swelling by evening. Pregnancy increases blood volume and puts pressure on the veins returning blood from the legs, making swelling common in the third trimester. Obesity adds sustained pressure on the veins and lymphatic vessels of the lower body, contributing to chronic low-grade swelling.
Infections
Cellulitis, a bacterial skin infection, causes swelling that’s concentrated in one area and comes with distinct signs: the skin is painful, red, swollen, warm to the touch, and tender. Unlike the gradual, painless swelling of vein problems or fluid retention, infection-related swelling develops over hours to days and is often accompanied by fever. The lower leg is one of the most common sites. Any break in the skin, even a small cut or crack between the toes, can serve as an entry point for bacteria.
How Doctors Assess Swelling
One of the first things a clinician does is press a finger into the swollen area for several seconds and watch what happens when they release it. If the pressure leaves a visible dent that slowly fills back in, that’s called pitting edema, and it’s graded on a scale from 1+ (a shallow dent of about 2 millimeters) to 4+ (a deep dent of 8 millimeters or more). Pitting edema is typical of fluid overload from heart, kidney, or liver problems, as well as vein disease and medication side effects.
Non-pitting edema, where the skin bounces right back, is more characteristic of lymphedema or thyroid disease. The distinction helps narrow down the cause, along with whether swelling is in one leg or both, how quickly it appeared, and what other symptoms are present.
Managing Swelling at Home
For mild swelling related to gravity, salt, or long periods of inactivity, a few strategies help. Elevating your legs above heart level allows gravity to work in your favor, draining fluid back toward the center of your body. Reducing sodium intake directly reduces the amount of fluid your body retains. Moving regularly, even short walks or calf raises, activates the muscle pump in your lower legs that pushes blood upward through the veins.
Compression stockings apply graduated pressure to the legs, with the most pressure at the ankle and less as the stocking goes up. Low-compression stockings (under 20 mmHg of pressure) are available without a prescription and work well for mild, gravity-related swelling. Stockings rated at 20 mmHg or higher require a prescription and are used for conditions like CVI or lymphedema. Getting the right fit matters, so it’s worth being measured rather than guessing a size.