When the white blood cell count in the surrounding blood continuously remains below 4.0*10^9/L, we call this condition leukopenia. Typical symptoms of leukopenia include dizziness, fatigue, limb soreness, reduced appetite, and listlessness, although some patients may not exhibit any obvious clinical symptoms. The causes of leukopenia are very complex and can be classified into two main categories: primary and secondary. Primary leukopenia refers to cases where the cause is unknown, while secondary leukopenia refers to cases potentially caused by acute infections or physical and chemical factors, or diseases of the hematopoietic system, connective tissue diseases, allergic diseases, or genetic diseases, all of which may lead to a reduction in white blood cells.