Swelling of one or both legs, which is clinically called leg edema, is a result of a buildup of fluid in the legs. Fluid leaks out from the bloodstream and pools in the tissues of the legs. The causes of leg edema can range from minor to serious and may be localized to the legs or a symptom of a problem in a distant organ.
Blood Clot
Normally, blood flows through blood vessels delivering oxygen to tissues and then returns to the lungs to pick up more oxygen. However, some health conditions cause the blood to clot in a blood vessel, causing what is clinically called a venous thrombosis.
The University of Southern California Center for Vascular Care describes two types of blood clots in the veins of the legs: superficial thrombophlebitis and deep vein thrombosis, both of which can cause leg edema. Superficial thrombophlebitis occurs when a blood clot forms in the superficial veins just beneath the skin, and may be caused by an injury or a varicose vein. Deep vein thrombosis is a life-threatening condition in which a blood clot forms in a vein deep in the leg. The blocked blood vessel prevents blood from returning to the heart. Additionally, the clot can break free and may become lodged in the lungs causing another serious condition called a pulmonary embolism. This condition is associated with underlying health conditions that cause the blood to flow sluggishly through the blood vessels.
Organ Failure
If swelling occurs in both legs, the cause is likely to be related to impaired organ functioning elsewhere in the body, according to MayoClinic.com. For example, impaired heart functioning can cause accumulation of fluid in the legs and is associated with other symptoms such as chest pain and shortness of breath. Additionally, one of the key functions of the kidney is to help maintain the appropriate amount of fluid circulating in the blood vessels. If the kidneys are not functioning properly, there may be an overabundance of circulating fluids, which may also cause leg edema. The buildup of fluid may also occur elsewhere in the body, but gravity when sitting or standing upright contributes to this fluid accumulation in the legs.
Medication
Leg edema is also a possible side effect of some medications. According to Drugs.com, medications that may cause leg edema include those that contain estrogen, such as hormone replacement therapy or birth control pills, or testosterone; antidepressant medications, especially tricyclics like nortriptyline or MAO inhibitors like phenelzine; steroids; and blood pressure medications that block calcium channels, such as nifedipine. Drugs.com advises contacting a medical professional if the swelling does not go away or becomes severe.
Other Causes
MedlinePlus, an online medical encyclopedia associated with the U.S. National Library of Medicine, describes other possible causes of leg swelling. Prolonged standing can cause even people with normal organ functioning to accumulate fluid in the legs. Additionally, prolonged periods of immobility, such as while traveling or if sick in bed with another health condition, can also prevent optimal circulation and thus buildup of fluid in the legs. Leg edema also sometimes occurs in pregnant women. If this swelling is excessive, it may be a sign of a serious condition called preeclampsia that also causes high blood pressure. Lastly, leg edema is also often caused by injury to the knee or leg.
