What causes mild eosinophilia?

Eosinophils are a type of white blood cell. The normal range of eosinophils is zero to 400 eosinophils per microliter of blood. In some laboratories up to 500 is still considered normal. Mild eosinophilia is not strictly defined. Eosinophil counts between 400 to 750 are common, and happen most often in people with allergies, asthma, eczema, or parasitic infections. Medication reactions are also a common reason for mild eosinophilia.