Normally, low white blood cells may be caused by physiological factors, and may also be caused by pathological factors such as viral infections, leukemia, and systemic lupus erythematosus. 1. Physiological factors: Generally, normal people will have low white blood cells when they are tired or hungry, and can increase white blood cells through proper rest and supplementation. 2. Pathological factors: low leukocytes may suggest the possibility of serious infection, leukemia, aplastic anemia, systemic lupus erythematosus and other diseases. (1) Infection: Severe infections can lead to low white blood cells. Low white blood cells can also occur when the body’s immunity is lowered, indicating a more serious condition. (2) Leukemia: Leukemia is usually caused by biological and genetic factors, and is often accompanied by symptoms such as high fever and skin purpura, and often manifests itself as a decrease in white and red blood cells. (3) Aplastic anemia: it can be caused by bone marrow hematopoietic failure leading to a decrease in white blood cell count, accompanied by a decrease in hemoglobin and platelet indices. (4) Systemic lupus erythematosus: Systemic lupus erythematosus is usually caused by genetics, abnormalities in the immune system, etc. It is often accompanied by rashes, arthritis, etc., and manifests itself in the form of low white blood cell counts and thrombocytopenia. Low white blood cells can also be seen in other diseases or caused by chloramphenicol or chemotherapeutic drugs such as cyclophosphamide, etc. It is recommended to go to a professional hospital to clarify the cause of the disease and then under the guidance of the doctor for the next examination and treatment.