Edema is the buildup of excess fluid in the spaces between your cells, causing swelling you can usually see and feel. It most commonly shows up in the legs, ankles, and feet, but it can develop anywhere in the body, including the lungs, hands, and face. Sometimes edema is harmless and temporary, like swollen ankles after a long flight. Other times it signals a serious underlying condition that needs attention.
How Fluid Builds Up
Your body constantly moves fluid between your bloodstream and the surrounding tissues. Small blood vessels called capillaries release fluid into tissues to deliver nutrients, and the lymphatic system drains it back. Edema happens when this balance tips: either too much fluid pushes out of the capillaries, or not enough drains away.
Four things can throw off this balance. First, increased pressure inside the blood vessels can force more fluid out, which is what happens with heart failure or a blood clot. Second, low levels of protein in the blood (common in liver or kidney disease) reduce the blood’s ability to hold onto fluid, so it leaks out. Third, damage or inflammation can make capillary walls more “leaky,” allowing fluid to escape easily, as occurs during allergic reactions or infections. Fourth, a blocked or damaged lymphatic system can’t drain fluid properly, leading to a type of swelling called lymphedema.
Pitting vs. Non-Pitting Edema
One of the first things a doctor checks is whether swelling “pits.” If you press a finger into the swollen area for a few seconds and it leaves a visible dent, that’s pitting edema. It’s graded on a four-point scale based on how deep the dent is and how long it takes to bounce back:
- Grade 1: A 2 mm dent that rebounds immediately
- Grade 2: A 3 to 4 mm dent that rebounds in under 15 seconds
- Grade 3: A 5 to 6 mm dent that takes 15 to 60 seconds to rebound
- Grade 4: An 8 mm dent that takes two to three minutes to rebound
Pitting edema typically results from conditions that raise pressure in the veins or reduce protein in the blood, such as heart failure, deep vein thrombosis, or kidney disease.
Non-pitting edema feels firmer and doesn’t leave a dent. Lymphedema is the most common cause. It develops when lymph vessels or lymph nodes are damaged, often after surgery, radiation therapy, or tumor growth. Primary lymphedema, where the lymphatic system doesn’t develop properly, is rare, affecting roughly 1 in 100,000 people. Severe thyroid disease can also cause non-pitting swelling called myxedema, which appears in the shins or more broadly across the body depending on whether the thyroid is overactive or underactive.
Common Causes
The list of conditions that cause edema is long, but a few stand out as the most frequent.
Heart failure is one of the major drivers. When the heart can’t pump blood effectively, pressure rises in the veins, pushing fluid into surrounding tissues. At the same time, reduced blood flow to the kidneys triggers hormonal signals that tell the body to hold onto sodium and water, compounding the problem. The result is swelling in the legs, ankles, and sometimes the abdomen, along with the risk of fluid backing up into the lungs.
Kidney disease works through a similar mechanism. When the kidneys can’t filter blood efficiently, sodium and water accumulate in the body, increasing blood volume and driving fluid into the tissues. Kidney disease can also cause protein to spill into the urine, lowering protein levels in the blood and further weakening the body’s ability to keep fluid inside the bloodstream.
Liver disease, particularly cirrhosis, reduces the liver’s production of blood proteins. This drop in protein allows fluid to leak out of blood vessels. Liver disease also raises pressure in the veins that drain the digestive system, which can cause fluid to collect in the abdomen, a condition known as ascites.
Venous insufficiency is one of the most common causes of chronic leg swelling. When the valves in leg veins weaken, blood pools in the lower legs, raising pressure in the capillaries. Over time you may notice not just swelling but also brownish discoloration of the skin around the ankles from iron deposits left by leaking red blood cells.
Medications That Cause Swelling
Several widely prescribed medications can cause edema as a side effect, and it’s worth knowing which ones since the swelling sometimes gets mistaken for a new health problem.
Blood pressure medications in the calcium channel blocker family are among the most common culprits. They widen the arteries feeding into capillaries without equally affecting the veins, which raises pressure inside the capillary bed and pushes fluid out. The swelling is dose-dependent, meaning higher doses cause more noticeable ankle and foot puffiness. It’s a frequent enough problem that many patients stop taking these medications because of it.
Diabetes medications in the thiazolidinedione class cause edema in 3% to 5% of people when used alone, but the rate climbs to 13% to 16% when combined with insulin. These drugs increase both vascular permeability and sodium retention in the kidneys.
Other medications linked to edema include NSAIDs (like ibuprofen and naproxen), which reduce kidney filtration and promote sodium retention. Nerve pain medications such as gabapentin and pregabalin, corticosteroids, certain antipsychotics, and dopamine-related drugs used for Parkinson’s disease can all contribute to swelling as well. If you notice new swelling after starting a medication, that connection is worth raising with your prescriber.
When Edema Affects the Lungs
Pulmonary edema, fluid in the lungs, is a different and more dangerous situation than swollen ankles. When fluid fills the tiny air sacs in the lungs, it directly interferes with breathing.
Acute pulmonary edema comes on fast. The hallmark symptoms are severe shortness of breath that worsens when lying down, a feeling of drowning or suffocating, a cough that produces foamy or blood-tinged sputum, and wheezing. This is a medical emergency.
Chronic pulmonary edema develops more gradually. People often notice waking up at night short of breath, needing extra pillows to sleep comfortably, worsening breathlessness with physical activity, wheezing, and progressive swelling in the legs, feet, and belly. These symptoms tend to creep up slowly enough that people adjust to them without realizing how much their breathing has deteriorated.
Symptoms That Need Urgent Attention
Most edema develops slowly and isn’t immediately dangerous, but certain patterns are red flags. Shortness of breath, chest pain, or an irregular heartbeat alongside swelling can indicate fluid in the lungs and needs immediate medical evaluation. Sudden swelling in one leg, particularly if it’s painful and warm, may indicate a deep vein thrombosis (blood clot), especially after prolonged sitting such as a long flight. Rapid, unexplained swelling with sudden weight gain over a day or two can signal worsening heart or kidney function.
Managing Everyday Edema
For mild to moderate swelling, especially the kind related to prolonged sitting or standing, venous insufficiency, or pregnancy, a few practical strategies make a real difference.
Compression stockings are one of the most effective tools. Even light compression in the 10 to 15 mmHg range reduces swelling from prolonged sitting or standing. Stockings in the 15 to 20 mmHg range provide a significant reduction, and the 20 to 30 mmHg range offers even more benefit. You don’t necessarily need the highest pressure to see results. Calf-length stockings in the 11 to 21 mmHg range can reduce or fully prevent occupational swelling in people who sit or stand for long stretches.
Reducing sodium intake helps your body hold onto less water. A common target is staying under 2,000 milligrams of sodium per day. Since most dietary sodium comes from processed and restaurant foods rather than the salt shaker, reading labels is more useful than simply not salting your meals.
Elevating swollen legs above heart level for 15 to 30 minutes several times a day lets gravity assist with drainage. Regular movement, even short walks or calf raises, activates the muscle pump in your lower legs that pushes blood back toward the heart. Sitting still for hours is one of the simplest ways to worsen leg swelling, so periodic movement throughout the day matters more than most people realize.
For edema caused by an underlying condition like heart failure, kidney disease, or liver disease, managing the root cause is what ultimately controls the swelling. Doctors often prescribe water pills (diuretics) to help the kidneys excrete excess fluid, but these work best as part of a broader treatment plan that addresses why the fluid is accumulating in the first place.