Eosinophilia (eosinophilic leukocytosis) is an increase in the blood level of eosinophils more than 500 in 1 μl of blood or more than 5%. Most often occurs in allergic reactions, parasitic invasions, may indicate severe lung diseases, oncological hematological pathologies. There are no specific manifestations. The clinical picture depends on the disease in which there is an increased content of eosinophils. The level of eosinophils is examined in venous or capillary blood by counting the leukocyte count in the general blood test. To correct eosinophilia, it is necessary to treat the disease that caused it.