Swollen legs and feet happen when excess fluid builds up in the tissue beneath your skin, a condition called peripheral edema. The cause can be as simple as sitting too long or as serious as a heart or kidney problem. Whether the swelling is in one leg or both, appeared suddenly or crept in over weeks, tells you a lot about what’s behind it.
Your body constantly moves fluid between your bloodstream and the surrounding tissue. Swelling occurs when that balance tips: pressure inside your blood vessels rises too high, your veins or lymph channels can’t drain properly, or your blood doesn’t have enough protein to hold fluid inside the vessels. Understanding which of these is happening points to the likely cause.
Swelling in Both Legs vs. One Leg
This is the single most useful distinction. Swelling in both legs at the same time usually points to a whole-body issue: heart failure, kidney disease, liver disease, a medication side effect, or chronic vein problems. Swelling in just one leg is more likely a local problem, such as a blood clot, an injury, or an infection. About 75% of blood clots in the legs affect only one side, with the left leg involved more often than the right.
If both legs are swollen and you also notice puffiness in your face or hands, that pattern suggests a kidney or liver issue rather than a vein problem. If the swelling is only below the knees and worse at the end of the day, venous insufficiency or prolonged standing are more likely explanations.
The Most Common Causes
Chronic Venous Insufficiency
This is the most frequent reason for persistent leg and foot swelling, especially in people over 50. The valves inside your leg veins weaken over time and stop pushing blood efficiently back toward the heart. Blood pools in the lower legs, and the increased pressure forces fluid into the surrounding tissue. Early on, you may just feel achy or heavy legs with no visible changes. As it progresses, you’ll notice skin discoloration, visible veins, and swelling that worsens through the day and improves overnight.
Heart Failure
When the heart can’t pump strongly enough, blood backs up in the veins. That backup reaches the legs and feet, causing swelling that’s often worse in the evening and leaves a temporary dent when you press on it (called pitting edema). You might also notice shortness of breath, especially when lying flat, or unexplained weight gain over a few days from fluid retention.
Kidney Disease
Healthy kidneys keep protein in your blood and filter out excess fluid. When they’re damaged, protein leaks into the urine, and your blood loses the ability to hold fluid inside the vessels. The result is widespread swelling, often starting around the eyes and ankles. Nephrotic syndrome, the more severe form of this, is defined by losing more than 3 grams of protein in the urine over 24 hours, along with low blood protein levels.
Liver Disease
Advanced liver disease reduces your body’s production of albumin, the main protein that keeps fluid inside blood vessels. It also raises pressure in the veins draining the abdomen. Both effects push fluid into the legs and belly. Swelling from liver disease is often accompanied by a visibly distended abdomen.
Hypothyroidism
Severe, untreated underactive thyroid can cause a distinctive type of swelling that feels firm and doesn’t leave a dent when pressed. It’s typically accompanied by other thyroid symptoms: feeling cold, constipation, slow heart rate, and weight gain.
Medications That Cause Swelling
Several common medications cause fluid retention in the legs and feet. If your swelling started within weeks of beginning a new drug, the medication itself may be the cause.
- Blood pressure medications (calcium channel blockers): Drugs like amlodipine and nifedipine are among the most common culprits. They widen the small arteries feeding into your capillaries, which raises the pressure inside those capillaries and pushes fluid into the tissue. This type of swelling is dose-dependent, meaning it’s worse at higher doses.
- Diabetes medications (thiazolidinediones): Pioglitazone and similar drugs cause the body to retain sodium and water while also making blood vessel walls more permeable to fluid.
- Anti-inflammatory drugs (NSAIDs): Ibuprofen and naproxen promote salt and water retention when used regularly.
- Steroids: Prednisone and similar corticosteroids cause fluid retention, particularly with long-term use.
Never stop a prescribed medication on your own because of swelling. But it’s worth flagging the timing with your doctor, because switching to a different drug in the same class often resolves the problem.
Pregnancy-Related Swelling
Some swelling in the legs and feet during pregnancy is normal, especially in the third trimester. Your blood volume increases significantly, and the growing uterus puts pressure on the veins returning blood from your legs.
What’s not normal is sudden, severe swelling, particularly if it appears in your face and hands as well. This pattern can signal preeclampsia, a dangerous condition involving high blood pressure that typically develops after 20 weeks of pregnancy. Other warning signs include severe headaches, vision changes like blurriness or light sensitivity, pain under the ribs on the right side, and nausea. Preeclampsia requires prompt medical attention because it can harm both the mother and baby.
When Swelling Is an Emergency
Sudden swelling in one leg that comes with pain, warmth, or redness may be a deep vein thrombosis (DVT), a blood clot in a deep vein. This is more likely if you’ve recently been immobile for a long period (a long flight, bed rest after surgery, or wearing a cast), have active cancer, or have had a blood clot before. The classic sign is calf swelling more than 3 centimeters larger than the other leg, with tenderness along the inner thigh or calf. A DVT is dangerous because a piece of the clot can break off and travel to the lungs.
Sudden swelling in both legs alongside shortness of breath and rapid weight gain (several pounds in a few days) can indicate acute heart failure. This also warrants emergency care.
What Helps Reduce the Swelling
The right approach depends entirely on the cause, but several strategies help with most types of leg and foot swelling.
Elevating your legs above heart level for 20 to 30 minutes a few times a day uses gravity to drain fluid back toward the center of your body. This works best for swelling from venous insufficiency, prolonged standing, or mild fluid retention. Walking and flexing your calves regularly throughout the day also helps because your calf muscles act as a pump for your veins.
Compression stockings apply steady, graduated pressure that supports your veins and prevents fluid from leaking into the tissue. Low-pressure stockings (under 20 mmHg) work for mild swelling and are available without a prescription. Medium-pressure stockings (20 to 30 mmHg) are more effective for moderate swelling or chronic venous insufficiency. High-pressure options (above 30 mmHg) are reserved for more advanced conditions and typically require a fitting from a healthcare provider.
Reducing salt intake helps because sodium causes your body to retain water. This is particularly important if your swelling is related to heart, kidney, or liver issues, where even modest salt reduction can make a noticeable difference in fluid balance.
How Doctors Figure Out the Cause
If your swelling is persistent, getting worse, or came on suddenly, your doctor will typically start with a physical exam focusing on whether the swelling is pitting (leaves a dent) or non-pitting, one-sided or both, and whether you have other symptoms like shortness of breath or changes in urination.
Basic blood work usually includes a chemistry panel to check kidney function, protein and albumin levels in the blood (low albumin points to kidney or liver disease), and liver enzymes. A urinalysis checks for protein leaking into the urine. If heart failure is suspected, imaging of the heart and a chest X-ray help assess how well the heart is pumping and whether fluid is accumulating in the lungs. For suspected blood clots, an ultrasound of the leg veins is the standard test.
The pattern of your swelling, combined with these results, usually identifies the cause. In many cases, particularly for people who stand or sit for long hours and notice swelling that resolves overnight, the answer is simply gravity and venous pressure doing what they do, and lifestyle changes like compression, movement, and elevation are enough to manage it.