The formation and accumulation of an abnormally high number of eosinophils (a type of white blood cell) in the blood or body tissues. Eosinophils are created in the bone marrow and are found in the bloodstream and the gut lining. They contain proteins that help the body to fight infection from parasitic organisms, such as worms. In certain diseases, however, these proteins can damage the body. Eosinophilia only indicates an increase in the number of eosinophils.