Edema is swelling of both legs from a buildup of extra fluid. Edema has many possible causes: Prolonged standing or sitting, especially in hot weather, can cause excess fluid to accumulate in the feet, ankles and lower legs. Tiny valves inside the veins of the legs can become weakened, causing a common problem called venous insufficiency. This problem makes it more difficult for the veins to pump blood back to the heart, and leads to varicose veins and buildup of fluid. Severe chronic (long-term) lung diseases, including emphysema and chronic bronchitis, increase pressure in the blood vessels that lead from the heart to the lungs. This pressure backs up in the heart. The higher pressure causes swelling in the legs and feet. Congestive heart failure, a condition in which the heart can no longer pump efficiently, causes fluid buildup in the lungs and other parts of the body. Swelling is often most visible in the feet and ankles. Pregnancy can cause edema in the legs as the uterus puts pressure on the vena cava, a major blood vessel that returns blood to the heart from the legs. Fluid retention during pregnancy also can be caused by a more serious condition called preeclampsia. Low protein levels in the blood caused by malnutrition, kidney and liver disease can cause edema. The proteins help to hold salt and water inside the blood vessels so fluid does not leak out into the tissues. If a blood protein, called albumin, gets too low, fluid is retained and edema occurs, especially in the feet, ankles and lower legs.
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