What is lymphedema? Lymphedema refers to the chronic accumulation of lymphatic fluid within soft tissues of the body that causes swelling of the affected area. It is usually identified in the extremities (i.e., arms or legs) but can be found anywhere in the body, including the face, oral cavity, neck, chest, and genitals. It is most widely identified in individuals with cancer; notably, one in five survivors of breast cancer will, later on, develop lymphedema. The lymphatic system is part of the immune system. It consists of lymphatic vessels that collect the excess interstitial fluid (i.e. fluid consisting of proteins, white blood cells, and water) that is not reabsorbed by the capillaries and returns it to the blood. Once the interstitial fluid is contained in the lymphatic vessels, the fluid is now called lymph. The lymph enters the lymphatic system through the lymphatic capillaries that then drain into larger lymphatic trunks and nodes. This flow is accomplished by the pulse of nearby arteries, neighboring muscles' contractions, and valves present within the lymphatic vessels. Lymphedema can be classified as either primary or secondary, depending on the origin of the condition. Primary lymphedema is a rare, inherited condition that affects 1 in 100,000 individuals. It results from errors in lymphatic development and can present at different stages of life. On the other hand, secondary lymphedema is much more common, seen in approximately 1 out of 1,000 people. Typically, it is the result of injury or obstruction to a fully developed lymphatic system.