The balance and regulation of fluid in the body is very complex. In short, the cause of edema as simply defined as possible, is that tiny blood vessels in the body (capillaries) leak fluid into the surrounding tissues. This excess fluid causes the tissues to swell.
The cause of fluid leaking into the surrounding tissues may be the result of several mechanisms, for example:
- too much force, or pressure inside the blood vessels;
- a force outside of the blood vessel causes the fluid to be drawn through it; or
- the wall of the blood vessel is compromised and cannot maintain equilibrium, leading to fluid loss.
Each of these three mechanisms may be associated with a variety of diseases or conditions. Examples include the following.
- Pregnancy: Edema during pregnancy may occur because pregnant women have a greater volume of fluid circulating in the body, and because they also retain more fluid. A woman may also experience postpartum edema.
- Medications: Edema may be caused by a variety of medications, for example, steroids, calcium channel blockers (CCBs), thiazolidinediones, nonsteroidal antiinflammatory drugs (NSAIDs), estrogens, etc.).
- Liver disease and/or kidney disease: Both of these organs are vital in maintaining fluid balance in the body, and if severe disease is present in either of these organ systems, edema can develop. Examples include: cirrhosis of the liver, chronic kidney disease, and acute kidney failure.
- Venous insufficiency: This is a common condition in which blood does not return to the heart efficiently from the peripheral areas of the body (for example, the ankles, legs, feet, hands), which results in edema. This typically results in edema in both legs.
- Heart failure: If the heart is weak and cannot pump blood efficiently, blood will pool in particular areas of the body, which will cause fluid to leak from the blood vessels into the surrounding tissues.
- If the right side of the heart is weak, pressure will build in the peripheral tissues in the body (hands, ankles, feet, legs). This is referred to as peripheral edema.
- If the left side of the heart is weak, pressure will build in the lungs, causing pulmonary edema.
- Idiopathic edema: Accumulation of fluid in surrounding tissues with no identifiable cause is referred to as idiopathic edema.
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