Edema is swelling caused by excess fluid trapped in your body's tissues. Edema occurs when tiny blood vessels in your body (capillaries) leak fluid. The fluid builds up in surrounding tissues, leading to swelling. Although edema can affect any part of your body, it's most commonly noticed in the hands, arms, feet, ankles and legs.
Edema may be generalized or local. It can appear suddenly, but usually develops subtly - the patient may first gain weight, or wake up with puffy eyes.