A collection of dynamic, physiological states. An instance of AllergicReaction is an event in which an organism which is exposed to a particular substance (e.g., pollen, mold) develops some abnormality or impairment of its physiological condition as a result of interacting with the substance. Allergic reactions to some types of substances occur widely in members of a species; e.g., PoisonIvyPoisoning in humans. But other allergic reactions affect only a small proportion of a species, such as human allergies to penicillin. This concept is the collection of events in which allergic reactions are `taking place', not abstract unrealized potential situations such as `John is allergic to milk.' I.e., if John were allergic to milk, and he drank some, and then proceeded to have a whopping bad allergic reaction, that latter event would be an instance of AllergicReaction.