What may happen in the body that triggers late onset allergies?

More symptoms: Many allergic reactions are biphasic meaning that immediate symptoms that resolve after a few hours are followed 6-10 hours later by the reappearance of symptoms without additional exposure to the allergic trigger. The symptoms are the same but may be more intense & last longer in the late phase. Prompt early treatment with topical corticosteroids usually prevent late onset symptoms.

Allergies: It is believed that this is a function of a certain type of cell called the basophil. It can also be a delayed type hypersensitivity reaction which is mediated by t-cells in the immune system. http://pathmicro.med.sc.edu/bowers/immune%20cells.htm.