How Edema Works

In years gone by, when someone's lower legs, ankles and feet were swollen, people called it "dropsy." Today, however, we call it edema. It's important to note that edema isn't a disease, but the symptom of an underlying condition, like heart failure (in which the heart is not pumping well enough to meet the body's demand for oxygen).

Edema is swelling caused by fluid (primarily water) that gets trapped in the tissues of your body. It usually occurs in the feet, ankles and legs (where it's called peripheral edema), but it also can occur nearly anywhere in the body, including the lungs (pulmonary edema) and the abdomen (ascites).

In most cases, edema begins when fluid leaks from the body's smallest blood vessels into the surrounding tissues. When the body senses that fluid is being lost from these vessels, it signals the kidneys to hold on to more fluid, increasing the volume of fluid in the vessels and leading to additional leakage.

Edema can occur if you sit or stand in one place for too long, as gravity pulls water down into your legs and feet. It can also result from a weakening in the valves of the veins in your legs, making it harder for them to push blood back up to the heart. Pregnant women sometimes get edema, and people who eat a diet too high in sodium (salt) can also develop it.

Certain diseases, such as kidney or liver disease, can cause edema or make it worse. One of the most common -- and most serious -- causes of edema is heart failure. In heart failure, the heart is weakened and its pumping action is impaired. There are two types of heart failure, based on which side of the heart is most affected. Each type is associated with a different type of edema:

  • Right-sided heart failure happens when the right chamber of the heart is not pumping adequately. As a result, the oxygen-poor blood that normally travels from the rest of the body to the heart begins to get backed up, causing fluid buildup in the veins and edema in the legs, ankles, and feet. Sometimes, right-sided heart failure can cause swelling in the abdomen (ascites).
  • Left-sided heart failure occurs when the left chamber of the heart cannot adequately pump oxygen-rich blood from the heart to the rest of the body. As a result, the oxygen-rich blood that normally travels from the lungs to the heart begins to get backed up, leading to the buildup of fluid in the lungs (pulmonary edema). Additional symptoms of left-sided heart failure include shortness of breath, fatigue and coughing, especially at night or while lying down.

­Signs that you might have edema include:

  • Stretched and shiny-looking skin over a swollen area
  • Increased abdomen size (ascites)
  • Shortness of breath or difficulty breathing (­pulmonary edema)
  • Tightness of jewelry, clothing or accessories
  • Low output of urine, even when you are drinking as much fluid as normal
  • A dimple in the skin covering the swollen area that remains for a few seconds after a pressing finger has been released

People who have a more serious form of edema (for example, pulmonary edema) may also experience the following:­

  • Rapid and labored breathing
  • Shortness of breath (especially at night and/or while lying down)
  • Coughing, sometimes with frothy blood
  • ­A sense of feeling suffocated