DAO and food allergy: A harmful role for estrogen signaling in the setting of a food allergy is that an increased estrogen increases the level of immunoglobulin and impaired B cell function (35, 36), in addition, estrogen stimulates mast cells to release histamine and down-regulates the DAO enzyme that clears histamine, at the same time, histamine stimulates the ovaries to produce more estrogen (37, 38).