When von Pirquet coined the term "allergy" at the beginning of this century, he had in mind a general designation of "altered reactivities" to external stimuli. Some responses may be beneficial to the host, ie, prophylactic, Whereas other responses may be harmful or anaphylactic. By common usage, "allergy" has come to mean a group of human diseases based on exaggerated immune responses to inhaled, ingested, or injected foreign substances. The most striking of these overexuberant responses are attributable to elevated production of antibodies of the IgE class, although other immunoglobulin classes are known to produce signs of allergy. Sometimes other mechanisms are involved, including the production of immune complexes and of antigenspecific effector T cells. Allergy as a medical specialty, then, has grown up around the diagnosis and treatment of this group of disorders.
The fact that allergy is a medical specialty based on etiology rather than on anatomic location