Neutrophils are a type of white blood cell that make up the most abundant type of granulocytes and 40% to 70% of all white blood cells in humans. They are an essential part of the innate immune system, with their functions varying in different animals. Neutrophils are normally found in the bloodstream and are one of the first responders of inflammatory cells to migrate toward the site of inflammation during the beginning phase of inflammation, particularly as a result of bacterial infection, environmental exposure, and some cancers. They are capable of ingesting microorganisms or particles and can internalize and kill many microbes. Neutrophils are made in the bone marrow and travel throughout the body in the blood, tissues, and lymph nodes. They help capture and destroy invading bacteria or microorganisms by setting traps and ingesting them. Neutrophil levels can rise or fall in response to infections, injuries, drug treatments, certain genetic conditions, and stress. A high neutrophil count is called neutrophilia or neutrophilic leukocytosis and can be caused by a lot of different conditions, including infection, inflammation, and tissue damage from burns, surgery, or trauma. A low neutrophil count is called neutropenia and can be caused by a variety of factors, including viral infections, chemotherapy, and autoimmune disorders.