A low white blood cell (WBC) count, called leukopenia, can be caused by viral infections (like flu or hepatitis), certain medications (such as chemotherapy, antibiotics, or immunosuppressants), autoimmune diseases, bone marrow disorders, or nutritional deficiencies (like vitamin B12 or folate deficiency). When WBC levels are low, the body’s ability to fight infections weakens, which can lead to symptoms such as frequent or unusual infections, fever, sore throat, fatigue, and slow recovery from illness. You should seek further medical evaluation and blood tests if the low count is persistent, very low, or accompanied by repeated infections or unexplained symptoms, so doctors can identify the underlying cause and decide whether treatment or monitoring is needed.