Hypereosinophilia is a medical condition characterized by an unusually high number of eosinophils, a type of white blood cell, in the bloodstream. Eosinophils play a crucial role in the body's immune response, particularly in fighting off parasitic infections and in allergic reactions. When their levels exceed normal ranges, it can indicate underlying health issues, including infections, allergies, or certain cancers. The causes of hypereosinophilia can vary widely and may include allergic disorders, autoimmune diseases, or parasitic infections. In some cases, it may be idiopathic, meaning the cause is unknown. Symptoms can range from mild to severe and may include skin rashes, respiratory issues, or gastrointestinal problems, depending on the underlying cause.