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How can chemotherapy cause leukopenia?

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Illustration of a blood vessel with a cutaway view showing red blood cells, white blood cells, platelets, and plasma, each labeled to highlight the main components of blood. — white blood cell Blood is made up of multiple components, including red blood cells, white blood cells, platelets, and water-rich plasma.

Chemotherapy causes leukopenia primarily through toxic damage to the bone marrow.1

Bone marrow contains hematopoietic stem cells responsible for producing white blood cells, which are essential for fighting infection. Because chemotherapeutic agents are designed to target rapidly dividing cells, they often inadvertently damage these blood-forming cells within the marrow cavities. This suppression of marrow function leads to a reduction in the production of leukocytes, resulting in an abnormally low count in the blood circulation.213

While this effect is a common and serious side effect of chemotherapy, particularly when treating cancer such as leukemia, it significantly increases a patient's susceptibility to infections. In some cases, medical professionals may use stem cell therapy or bone marrow transplantation to help restore the blood-making system after aggressive treatment.12