Allergy Definition

The term "allergy" was originally introduced by von Pirquet in 1906, meaning "changed reactivity". At that time he imposed no restrictions as to the type of immunological response in the patient. It is only in recent years that "allergy" has become synonymous with Type I hypersensitivity (IgE-mediated allergy). Four different types of hypersensitivity were described by Coomb and Gell (Types I, II, III and IV), as a pedagogical way to increase the understanding of different immune reactions which could be provoked by many antigens. In practice these types do not necessarily occur in isolation from each other.

 

Allergic diseases generally begin in childhood, although they can arise at any age. Development of allergic disease is associated with an allergic constitution due to heredity and to environmental and health factors.

 

The allergic constitution is called atopic and reflects an increased production of allergen-specific IgE antibodies, which may lead to clinical symptoms such as rhinitis, asthma, eczema, colic pains or diarrhea. A state of hyperreactivity often accompanies an allergic reaction. If this hyperreactivity occurs in the respiratory tract, everyday stimuli like dust, tobacco smoke, cold air and perfumes may lead to allergy-like symptoms.