The possible causes of eosinophil percentage 40 are allergic diseases, parasitic infections, blood diseases, skin diseases and so on. 1. Allergic diseases: such as urticaria, bronchial asthma and other diseases, peripheral eosinophils can be significantly increased. When the allergy is controlled, the proportion of eosinophils will gradually return to the normal level. 2. Parasitic infections: common schistosomiasis, ascariasis, liver fluke and so on, can make the blood eosinophils increased significantly. Parasitic infections must be treated. 3. Blood diseases: eosinophilic leukemia, for example, can increase peripheral eosinophils to varying degrees. If necessary, bone marrow cytology should be performed to determine the type of disease and further treatment. 4. Skin diseases: such as eczema, exfoliative dermatitis, psoriasis, etc., can also cause peripheral eosinophils to rise. At this point, it is necessary to actively treat the skin disease. The patient’s eosinophil percentage of 40 may also be other reasons, then you need to consult a doctor in a timely manner to find out the cause of the disease, under the guidance of the doctor for treatment. At the same time, it is necessary to follow the doctor’s instructions for regular review and dynamic observation of the effect of treatment.