The causes of low neutrophils are mainly drug factors, disease factors, physiologic factors, infections, and physical factors of injury. 1. Drug factors: the most common antibiotic treatment is the application of cephalosporin antibiotics, which can cause neutrophil decline in some people. Tumor patients in the application of chemotherapeutic drugs, or local radiotherapy after 1~2 weeks or 1 month, may also cause bone marrow inhibition and cause significant neutrophil decline. 2. Disease factors: Cirrhosis of the liver can lead to hypersplenism, there will also be a decline in neutrophils, while the total number of white blood cells and platelets will fall. Aplastic anemia can also lead to hematopoietic hypoplasia, resulting in neutropenia. Autoimmune diseases can lead to destruction or excessive depletion of neutrophils, resulting in low neutrophils. 3. Physiological factors: If the body is weak, such as the elderly, there will be a mild decline in neutrophils. 4. Infections: Infections can lead to destruction or excessive consumption of neutrophils, resulting in low neutrophils. 5. Physical damage: such as radiation exposure, may also lead to low neutrophils. Overall, if there is a decline in neutrophils, it is necessary to analyze the specific situation of the patient, and after clarifying the cause, to carry out appropriate treatment under the guidance of the doctor.