Most diseases can cause low white blood cells, such as typhoid infection, aplastic anemia, partial leukemia and systemic lupus erythematosus. 1. Typhoid fever or paratyphoid infection will lead to a decrease in the total number of white blood cells and neutrophils, resulting in low white blood cells, accompanied by weakness, dizziness, nausea, vomiting and other clinical symptoms. 2. When aplastic anemia occurs, the number of red blood cells, white blood cells and platelets will be reduced, resulting in low white blood cells, accompanied by dizziness and bleeding on the surface of the skin and mucous membranes. 3. Some leukemia patients do not have increased white blood cells at the onset of the disease, or even have low indicators, and there may be anemia, platelet reduction and other indicators of change. 4. Systemic lupus erythematosus can also cause low white blood cell count, and there can be fever, erythema multiforme and other manifestations. If there is a low white blood cell count, it is recommended to consult a regular hospital as soon as possible for a clear diagnosis and standardized treatment under the guidance of a doctor.