Lymphedema, is a one-word way of saying swelling that results from lymph fluid in your body. It can happen anywhere in your body, though it’s usually in your arms or legs. According to the Centers for Disease Control and Prevention (CDC), lymph fluid is the part of the system that carries fluids and cells that help fight infection. When those fluids get built up (such as when you’re fighting cancer!), they cause swelling, which can happen in a flash or slowly, over a long period of time.