Chemotherapy (drugs used to kill cancer cells) can damage rapidly dividing normal cells, such as the hair follicle cells that grow hair and the bone marrow cells that produce white blood cells, in addition to killing cancer cells. This causes low white blood cell counts. When patients have low white blood cell counts, they are at risk of infection. A low neutrophil count is called neutropenia. Doctors carefully monitor the blood counts of patients receiving chemotherapy and also watch for signs of infection, including fevers. They may prescribe G-CSF to increase the number of neutrophils and reduce the risk of infection. Granulocyte colony-stimulating factor is also used for patients who are receiving a bone marrow transplant and for some blood cell cancers. Not all chemotherapy requires G-CSF treatment.