Swollen legs are usually caused by fluid pooling in the tissues of your lower body, a condition called peripheral edema. The cause can be as simple as sitting too long or eating a salty meal, or it can signal something more serious like a blood clot, heart failure, or kidney disease. One of the fastest ways to narrow down what’s going on is to notice whether the swelling affects one leg or both, since these point to very different problems.
When Both Legs Are Swollen
Swelling in both legs at once usually points to a systemic issue, meaning something affecting your whole body rather than one specific spot. The most common everyday causes are prolonged sitting or standing, high sodium intake, and medication side effects. These tend to produce mild, symmetrical puffiness that worsens through the day and improves overnight.
More serious causes of bilateral swelling include heart failure (where the heart can’t pump blood efficiently), chronic kidney disease, liver scarring (cirrhosis), and damage to the kidneys’ filtering vessels. In each of these conditions, your body either retains too much fluid or can’t circulate it properly, and gravity pulls the excess into your legs and ankles. If swelling in both legs persists for more than a few days, comes on suddenly, or is accompanied by fatigue, weight gain, or reduced urination, it’s worth getting checked out.
When Only One Leg Is Swollen
Swelling in a single leg is a different situation and deserves closer attention. The two most common causes are deep vein thrombosis (a blood clot in a deep leg vein) and cellulitis (a bacterial skin infection). Both can produce a swollen, red, painful leg, and they look similar enough that even clinicians have to run tests to tell them apart.
A blood clot in the leg is particularly concerning because a piece can break off and travel to the lungs, creating a life-threatening emergency called a pulmonary embolism. If one leg swells suddenly, feels warm, and hurts, especially after a period of immobility like a long flight or surgery, treat it as urgent. Other causes of one-sided swelling include a sprained ankle, a torn muscle, or a blocked lymph node on that side.
Venous Insufficiency: The Chronic Cause
If your legs have been swelling on and off for months or years, chronic venous insufficiency is one of the most likely explanations. Your leg veins contain one-way valves that help push blood upward against gravity, back toward your heart. When those valves weaken or get damaged, blood flows backward and pools in the lower legs. This backward flow is called venous reflux.
Over time, the constant pressure from pooled blood causes visible changes beyond just swelling. Tiny capillaries burst, leaving the skin with a reddish-brown discoloration, especially near the ankles. The skin can become flaky, itchy, or leathery in texture. In advanced cases, scar tissue traps fluid in the calf, making it feel large and firm to the touch. The skin becomes fragile and prone to open sores (venous ulcers) that are slow to heal. Risk factors include obesity, a history of blood clots, multiple pregnancies, and jobs that require long periods of standing.
Medications That Cause Swelling
Leg swelling is a surprisingly common side effect of many widely prescribed drugs. If your legs started puffing up after beginning a new medication, the timing alone may be your biggest clue. The most frequent culprits include:
- Blood pressure medications, particularly calcium channel blockers like amlodipine and nifedipine
- Anti-inflammatory drugs, including ibuprofen, naproxen, and prescription corticosteroids like prednisone
- Nerve pain medications like gabapentin and pregabalin
- Hormones, including estrogen, progesterone, and testosterone
- Diabetes medications like pioglitazone
If you suspect a medication is the cause, don’t stop taking it on your own. Your prescriber can often switch you to an alternative that doesn’t cause fluid retention.
Diet, Salt, and Fluid Retention
Your body carefully balances sodium and water. When you eat a high-sodium meal, your kidneys hold onto extra water to dilute the sodium, and that extra fluid ends up in your tissues. The swelling is typically mild and shows up in both legs, ankles, and sometimes the hands and face. It usually resolves within a day or two once sodium intake drops.
Reducing salt in your diet is one of the simplest ways to manage recurring mild edema. Most excess sodium comes from processed and restaurant foods rather than the salt shaker, so reading labels and cooking at home more often can make a noticeable difference.
Swelling During Pregnancy
Some leg and ankle swelling is completely normal during pregnancy, especially in the third trimester. Your body produces significantly more blood and fluid to support the baby, and the growing uterus puts pressure on the veins that return blood from your legs.
What isn’t normal is sudden, severe swelling, particularly if it shows up in your face and hands along with your legs. This pattern can be a sign of preeclampsia, a serious pregnancy complication involving high blood pressure. Sudden weight gain alongside the swelling is another red flag. Preeclampsia requires prompt medical treatment, so any rapid change in swelling during pregnancy warrants a call to your provider that same day.
How Doctors Assess Swelling Severity
When you see a provider about leg swelling, they’ll likely press a finger into the swollen area for a few seconds and watch what happens. If the pressure leaves a visible dent that takes time to spring back, that’s called pitting edema, and it’s graded on a 4-point scale. A grade 1 pit is just 2 millimeters deep and bounces back immediately. Grade 2 is 3 to 4 mm deep and rebounds in under 15 seconds. Grade 3 reaches 5 to 6 mm and takes up to a minute to fill back in. Grade 4, the most severe, leaves an 8 mm pit that takes two to three minutes to rebound.
This grading helps your provider track whether swelling is improving or worsening over time and guides decisions about treatment intensity.
What You Can Do at Home
For mild to moderate swelling without alarming symptoms, several strategies can provide real relief. Elevating your legs above the level of your heart for about 15 minutes, three to four times a day, helps gravity drain fluid back toward your core. Lying on a couch with your feet propped on a couple of pillows works well. Consistency matters more than duration here.
Compression stockings apply graduated pressure to your legs, squeezing tightest at the ankle and gradually loosening toward the knee or thigh. For mild everyday swelling, 15 to 20 mmHg stockings (labeled “mild support”) are usually enough. If you have chronic venous insufficiency or more persistent edema, a provider may recommend 20 to 30 mmHg (moderate) or 30 to 40 mmHg (firm) stockings. Higher compression levels should be fitted based on clinical assessment rather than guessed at.
Regular movement also helps. Walking activates the calf muscles, which act as a pump to push blood upward through your veins. If your job keeps you seated for hours, even flexing your ankles or taking a short walk every hour can reduce end-of-day swelling.
Symptoms That Need Immediate Attention
Most leg swelling isn’t an emergency, but certain combinations of symptoms call for urgent care. Call 911 or get to an emergency room if swollen legs are accompanied by chest pain, difficulty breathing, shortness of breath when lying flat, dizziness or fainting, or coughing up blood. These can indicate a blood clot in the lungs or a serious heart problem.
You should also seek same-day medical attention if the swelling comes on suddenly with no clear cause, follows a physical injury like a fall or car accident, or appears in only one leg with pain, pale skin, or a cool-to-the-touch feeling. One-sided swelling with these features raises concern for a blood clot that needs rapid diagnosis and treatment.