White blood cells are produced in the bone marrow. As they mature, white blood cells are continually released into the bloodstream. White blood cells circulate throughout the body, ready to fight infections. They live about two or three weeks, when they are broken down and recycled by the body. A normal white blood cell count is between about 4,500 and 10,000 cells per microliter. Many conditions can cause a low white blood cell count: • Infection (which usually increases the white blood cell count, but may decrease it). • Drugs, especially chemotherapy.