Causes of leukocyte lowering include infectious factors, physical and chemical factors, hypersplenism, immune diseases, blood diseases and so on. 1. Infectious factors: viral infection is a common cause of leukocyte lowering, such as chickenpox, rubella, viral hepatitis, influenza, etc., bacteria such as typhoid bacillus, paratyphoid bacillus and so on. 2. Physical and chemical factors: such as long-term exposure to radiation, chemotherapy, radiotherapy, etc., chemical drugs such as chloramphenicol, sulfonamides, anti-tumor drugs. 3. Hypersplenism: hypersplenism destroys white blood cells and platelets. 4. Immune diseases: such as systemic lupus erythematosus, rheumatoid arthritis and so on. 5. Diseases of the blood system: such as aplastic anemia, myelofibrosis, leukemia and so on. The lowering of white blood cells should seek medical advice in time, follow the doctor’s instructions for examination, clarify the cause of the disease and follow the doctor’s instructions for treatment.