A fall in the number of white blood cells — leucocytes — circulating in the blood to below the normal range. It leaves the body more vulnerable to infection and commonly results from viral illnesses, autoimmune disorders, bone marrow problems, chemotherapy, or certain medications. Because white blood cells are the front line of immune defence, people with leucopenia must take extra care with food hygiene, avoiding raw or undercooked foods that could carry pathogens their weakened defences cannot handle. Doctors monitor the count to adjust treatment and assess recovery. Nutritional support with adequate protein, vitamins, and minerals helps the bone marrow rebuild healthy cell production.