A swollen leg has dozens of possible causes, ranging from sitting too long on a flight to a serious blood clot. The single most important thing to figure out first is whether one leg is swollen or both, because that distinction points toward very different explanations. One-leg swelling usually means a local problem: a clot, an injury, or an infection. Both-leg swelling more often signals something systemic, like heart, kidney, or liver trouble, or a medication side effect.
One Swollen Leg vs. Both
When only one leg swells, the cause is typically something happening in that leg alone. A deep vein thrombosis (blood clot in a deep vein), a muscle injury, cellulitis (a skin infection), or a problem with the veins or lymphatic system on that side are the most common culprits. The swelling may come on suddenly or build over days, and it often comes with pain, warmth, or redness.
When both legs swell symmetrically, the problem is more likely body-wide. Fluid leaks from tiny blood vessels called capillaries and accumulates in the surrounding tissue. Heart failure, kidney disease, and liver damage can all drive this kind of swelling. So can medications and prolonged sitting or standing. Pregnancy is another common cause of bilateral leg swelling, especially in the third trimester.
Signs That Need Urgent Attention
A blood clot in a deep leg vein is the most dangerous local cause of a swollen leg. It typically causes swelling in one calf or thigh along with pain, warmth, and redness. The real danger is that the clot can break loose and travel to the lungs, a condition called pulmonary embolism. If you develop sudden shortness of breath, chest pain that worsens when you breathe in or cough, a rapid pulse, dizziness or fainting, or you cough up blood, that is a medical emergency.
A rapidly spreading area of redness, warmth, and tenderness on a swollen leg may be cellulitis. This bacterial skin infection presents as a poorly defined patch of red or pink skin that feels warm and painful to touch. Unlike a superficial rash with sharp borders, cellulitis affects deeper tissue and its edges blend gradually into normal skin. It can worsen quickly and needs antibiotics, so don’t wait to see if it improves on its own. Fever alongside a red, swollen leg makes infection even more likely.
Common Everyday Causes
Most leg swelling isn’t an emergency. Standing or sitting for long stretches, especially during travel or desk work, lets gravity pool blood and fluid in your lower legs. Eating a high-sodium meal can cause temporary fluid retention. A sprained ankle or strained calf muscle will swell as part of the normal inflammatory response. Hot weather dilates blood vessels near the skin’s surface, which also promotes mild swelling.
Several common medications cause leg swelling as a side effect. Blood pressure drugs in the calcium channel blocker family are among the most frequent offenders. Roughly 25% of people taking these drugs develop peripheral edema, and it’s a leading reason patients stop the medication. Diabetes drugs in the thiazolidinedione class cause edema in 3% to 5% of users on their own, and that rate climbs to over 13% when combined with insulin. Pain medications like ibuprofen and naproxen can contribute to swelling by affecting kidney function. Nerve pain drugs like gabapentin and pregabalin, certain Parkinson’s medications, and corticosteroids can also be responsible. If your swelling started after beginning a new medication, that connection is worth flagging to your prescriber.
Chronic Venous Insufficiency
If your leg has been swelling on and off for months or years, especially toward the end of the day, chronic venous insufficiency is a leading possibility. This condition affects an estimated 10% to 35% of U.S. adults. The valves inside your leg veins that normally push blood upward toward your heart become weak or damaged, allowing blood to flow backward and pool. A previous blood clot is one of the most common triggers for this valve damage.
Over time, the backed-up pressure forces red blood cells out of the veins and into the surrounding tissue. Iron deposits from those cells stain the skin a brownish color, especially around the inner ankle. The skin can thicken and harden as the fat layer underneath becomes fibrous. In advanced cases, this process leads to open sores called venous ulcers, which develop in 1% to 3% of people with the condition and are notoriously slow to heal. Swelling that has been present for a long time and is accompanied by skin darkening or texture changes around the ankles is a strong signal of venous insufficiency.
Swelling During Pregnancy
Some leg swelling during pregnancy is completely normal, particularly in the second and third trimesters, as your body retains extra fluid and the growing uterus puts pressure on pelvic veins. What is not normal is sudden swelling, particularly if it appears in your face and hands at the same time. Sudden puffiness combined with severe headaches, vision changes (blurring, light sensitivity, or temporary blind spots), upper abdominal pain on the right side, or nausea can indicate preeclampsia, a serious blood pressure condition that typically develops after 20 weeks. This requires prompt medical evaluation.
How to Check Your Swelling at Home
You can get a rough sense of severity with a simple test. Press your thumb firmly into the swollen area for about five seconds, then release. If a dent (pit) remains, you have what’s called pitting edema. The depth of the dent and how long it takes to refill give you a rough grade. A shallow 2-millimeter dent that bounces back immediately is mild (grade 1). A deeper dent of 3 to 4 millimeters that refills within 15 seconds is grade 2. If the pit is 5 to 6 millimeters deep and takes up to a minute to refill, that’s grade 3. An 8-millimeter pit that lingers for two to three minutes is grade 4, which represents significant fluid accumulation.
Not all swelling pits when you press it. Non-pitting swelling feels firm or rubbery and doesn’t leave a dent. This pattern is more typical of lymphedema (a lymphatic drainage problem) or certain thyroid conditions, and it warrants a different workup than standard fluid retention.
What Happens at the Doctor’s Office
If your swelling is new, one-sided, painful, or accompanied by other symptoms, your doctor will likely start with a physical exam and ask about your medical history, medications, and activity level. When a blood clot is suspected, a blood test called a D-dimer is often the first step. This test detects fragments of dissolved clots in your blood. A normal D-dimer result makes a clot very unlikely. An elevated result doesn’t confirm a clot (many things raise D-dimer levels), but it triggers the next step: an ultrasound of your leg veins. This painless imaging test uses sound waves to visualize blood flow and can directly show whether a clot is present.
For bilateral swelling, the focus shifts to the heart, kidneys, and liver. Blood tests, urine tests, and sometimes an echocardiogram (ultrasound of the heart) help identify whether one of these organs is struggling. Your doctor will also review your medication list carefully.
Managing Swelling at Home
For mild, non-urgent swelling, elevation is the simplest and most effective first step. Lie down and prop your leg above the level of your heart, using pillows or a cushion. This lets gravity help drain fluid back toward your center. Even 20 to 30 minutes a few times a day can make a noticeable difference.
Compression stockings apply gentle, graduated pressure that supports your veins and reduces fluid buildup. For everyday swelling related to prolonged standing or sitting, light compression in the 15 to 20 mmHg range is effective and comfortable enough to wear all day. Studies show this level significantly reduces occupational edema even within a single day of use. For more pronounced swelling or diagnosed venous insufficiency, your doctor may recommend 20 to 30 mmHg stockings, which provide stronger support. Put them on in the morning before swelling has a chance to build up.
Reducing sodium intake helps your kidneys release excess fluid rather than hold onto it. Moving your legs regularly, even just flexing your ankles or taking short walks, activates the calf muscle pump that pushes venous blood upward. If you sit at a desk all day, set a reminder to stand and walk for a few minutes every hour.