Eosinophils are a type of white blood cell produced in the bone marrow. They make up about 1 to 3% of the total number of white blood cells. Eosinophils can circulate in the blood and also are found outside blood vessels in other organs in the body. The gastrointestinal (GI) tract typically has the highest number of eosinophils relative to other organs.
Eosinophils protect the body killing bacteria and parasites, but can cause problems when they react incorrectly and cause allergies and other inflammatory reactions in the body. For example, food allergies can cause too many eosinophils to gather in the digestive tract, which may lead to symptoms such as diarrhea and damage to the cells lining the GI tract.
Eosinophils are part of the innate immune system, which means that they can "non-specifically" destroy any invaders that they encounter in the body, such as bacteria and parasites. Non-specifically means that eosinophils do not have to recognize the invader specifically, but instead simply recognize the invader as something that should not be present and should be destroyed.