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Why can neutropenia lead to frequent or severe bacterial infections?

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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.

Neutropenia leads to frequent or severe bacterial infections because it significantly reduces the body's primary defense against invading microorganisms.12

Neutrophils are a critical type of white blood cell that acts as a first responder to infection. They are actively phagocytic, meaning they migrate to sites of tissue injury or infection via chemotaxis to engulf and destroy bacteria. Once a bacterium is ingested, neutrophils use potent enzymes and highly active forms of oxygen, such as hydrogen peroxide, to digest and eliminate the pathogen.134

When a person has neutropenia—an abnormally low number of these cells—the body lacks a sufficient supply of these essential "phagocytic cells" to effectively identify, contain, and destroy invading bacteria. Consequently, the immune system's ability to mount an effective inflammatory response is compromised, leaving the individual highly vulnerable to persistent and life-threatening bacterial infections.123