Lymphedema occurs when lymph builds up in the body’s soft tissues, resulting in swelling. Lymph is a bodily fluid that contains white blood cells that fight infections. The build-up results from damage or blockage in the body’s lymph system, which prevents proper draining of lymph fluid. The swelling characteristic of lymphedema typically occurs in the arms or legs and may range in severity from barely noticeable to extreme. While the swelling tends to occur in just one arm or leg, it may affect both in some cases. In addition to visible swelling, lymphedema may cause feelings of tightness, aching, or heaviness in the affected limb; decrease range of motion; lead to recurring infections; or cause the skin on the affected area to harden and thicken. Causes of lymphedema include infection, cancer, scar tissue resulting from radiation therapy or lymph node removal, and genetic condition affecting the lymph nodes. In cases involving cancer treatment, the swelling may not occur for months or years afterwards. Treatment can help manage the symptoms of lymphedema and may include physical therapy exercises designed to move the fluid out of the affected area, use of bandages or compression devices to encourage lymph to flow out of the affected limb and back toward the trunk of the body, proper skin care, and massage—particularly a special type of massage known as manual lymph drainage.