Edema is a general term for swelling in the body due to the buildup of excess fluid in the tissues. It generally occurs when the pressure on oxygen-poor blood in the veins increases, and the fluid portion of the blood is forced out of the veins and into the surrounding soft tissues. This expands or swells the tissues. Edema is not a condition itself, but is the symptom of an underlying condition. Edema may occur in different parts of the body due to a variety of underlying causes, only some of which may be serious. For example, edema in the legs and ankles may be related to heart failure.

The most serious form of edema is pulmonary edema, a buildup of fluid in the lungs. Pulmonary edema is usually a sign of heart failure, in which the heart is not pumping well enough to meet the body’s demand for oxygen. Patients with pulmonary edema usually complain of shortness of breath.

Although pulmonary edema is most often caused by heart disease, it can also be caused by high altitude (above 8,000 feet). Accompanied by shortness of breath, pronounced weakness, and a cough that produces a white or frothy fluid, high altitude pulmonary edema (HAPE) is a life-threatening scenario requiring the individual to immediately descend and get prompt medical treatment.

Some common types of edema are as follows:

Edema can also be caused by factors such as medication use, burns, and conditions such as venous insufficiency. Venous insufficiency occurs when the veins of the leg no longer allow normal blood flow, usually because the valves in these veins stop functioning properly. Under normal circumstances, blood in the veins is only allowed to flow in one direction, back toward the heart. If, however, the valves are compromised for some reason, blood is allowed to flow backward, away from the heart. This raises blood pressure in the veins of the legs, which may lead to a variety of health problems, including edema, pain, discoloration or ulcers that do not heal.

Edema has also been shown to affect heart attack victims. During a heart attack, the heart sends a signal to the arteries near the site of the attack that promotes the growth of new blood vessels. The signal, however, also causes the arteries to become more permeable, so liquid can more easily leak through the blood vessel walls, resulting in edema. This edema continues to kill heart tissue even after blood flow is restored following the onset of the heart attack. Researchers are working to develop medications that reduce damage from this kind of edema, although the therapy is still experimental.