Edema is the atypical buildup of fluid in certain body tissues. The fluid retention may occur under the skin, especially in the legs or ankles, or in the lungs. This is generally caused by the body’s capillaries to leak fluid into surrounding tissues which leads to swelling. The specific mechanisms include an imbalanced pressure inside and outside blood vessels, and damaged blood vessel walls. Edema is often associated with pregnancy, heart failure, kidney problems, liver disease, and certain medications (steroids, nonsteroidal anti-inflammatory drugs, estrogens, etc.).