Eosinophils are a type of leukocyte that are called eosinophils because the cytoplasm of these cells is filled with eosinophilic granules that appear red after staining. Normally, eosinophils account for 0.5%-5% of all white blood cells, and more than 5% is an increase. There are various reasons for eosinophilia, the common reasons are as follows: First, various allergic diseases, such as bronchial asthma, urticaria, neurovascular edema, and various skin diseases such as eczema, psoriasis, etc., can have increased eosinophilia. Second, common parasitic infections, such as schistosomiasis, hookworm disease, ascariasis, etc., can also cause eosinophilia. Third, blood system diseases, such as chronic granulocytic leukemia, eosinophilic leukemia, lymphoma, myeloma, etc., can also cause eosinophil elevation.