Eosinophilia occurs regularly in a number of benign and malignant diseases. Occasionally, however, it may occur unexpectedly and without apparent cause. In these instances every effort should be made to determine the cause of the eosinophilia, in view of its frequent association with serious occult disease.
Wintrobe has listed the causes of eosinophilia as follows: (1) allergic disorders: bronchial asthma, urticaria, angioneurotic edema, and hay fever; (2) cutaneous diseases, especially pemphigus and dermatitis herpetiformis; (3) parasitic infestations, especially parasites which invade the tissues such as trichinae, echinococci, and, less regularly, intestinal parasites; (4) Loeffler's syndrome; "tropical eosinophilia"; (5) infections such as scarlet fever, chorea, erythema multiforme; (6) diseases of the hemopoietic system, namely, chronic myelocytic leukemia, erythremia, Hodgkin's disease, the postsplenectomy state, and pernicious anemia; (7) irradiation; (8) miscellaneous disorders such as periarteritis nodosa, tumors of the ovary or those involving serous surfaces or bones, sarcoidosis, and certain poisons; and
HILDEBRAND FL, CHRISTENSEN NA, HANLON DG. Eosinophilia of Unknown Cause. Arch Intern Med. 1964;113(1):129-134. doi:10.1001/archinte.1964.00280070131021