Eosinophils are a type of white blood cell that play a crucial role in the immune system. They are primarily involved in fighting off parasites and responding to allergic reactions. When the body detects allergens or infections, eosinophils are activated and move to the affected area, where they release substances to help combat these threats. These cells are characterized by their distinct orange-red granules when stained, which is how they got their name. High levels of eosinophils in the blood can indicate conditions like asthma or hay fever, while low levels may suggest other health issues. Understanding eosinophils helps in diagnosing and treating various allergic and inflammatory diseases.