Viral infections: Many viral infections, such as the flu or mononucleosis, can cause a temporary decrease in white blood cell count. This is often due to the virus's effect on the bone marrow or the immune system's response to the infection.

Medications: Certain medications, including antibiotics, antihistamines, and anti-inflammatory drugs, can suppress bone marrow activity, leading to a low WBC count.
Vitamin deficiencies: Deficiencies in vitamins like B12 or folate can impair the production of white blood cells.
Chronic diseases: Conditions such as chronic kidney disease, liver disease, or HIV/AIDS can lead to a low WBC count due to the body's decreased ability to produce new cells.
Aplastic anemia: A rare condition where the bone marrow fails to produce enough blood cells, including white blood cells.

Severe sepsis: In some cases, a low WBC count can be a sign of severe sepsis, where the body's immune response is overwhelmed by an infection. This is a life-threatening condition that requires immediate medical attention.
Leukemia: Certain types of leukemia, such as acute lymphoblastic leukemia (ALL), can cause a low WBC count. Early diagnosis and treatment are crucial for survival.
Bone marrow failure: Conditions like myelodysplastic syndrome (MDS) or bone marrow fibrosis can lead to a low WBC count and require prompt medical evaluation.

Congenital neutropenia: A rare genetic disorder characterized by a low WBC count from birth.
Cyclic neutropenia: A rare condition where the WBC count fluctuates periodically, often due to a genetic mutation.
Autoimmune disorders: Certain autoimmune conditions, such as rheumatoid arthritis or lupus, can cause a low WBC count in rare cases.
Radiation exposure: Exposure to high levels of radiation can damage the bone marrow, leading to a low WBC count.