Lower white blood cells can be a sign of viral infections, hematologic disorders, rheumatologic diseases, etc. Some of the leukopenia may also be caused by physiological phenomena or medication. 1. Viral infections: the most common clinical viral infections, such as influenza virus infection, rubella and so on, will appear low total white blood cell count. 2. Blood system diseases: such as aplastic anemia, due to bone marrow hematopoietic stem cell failure, white blood cell reduction is very obvious, accompanied by red blood cells, platelets and other indicators of common reduction. 3. Rheumatic immune diseases: such as rheumatoid arthritis, systemic lupus erythematosus, etc., white blood cells will also be reduced, but this performance is not specific. 4. Physiological phenomenon or due to medication: a transient decrease in white blood cells and no symptoms, may be normal fluctuations, belonging to the physiological. Taking certain drugs such as amoxicillin, propylthiouracil and exposure to radiation can also cause leukopenia. If leukopenia occurs, it is necessary to consult a doctor in a timely manner, analyze the situation rationally, find out the cause of the disease and carry out rational treatment.