There are different types of allergy. The immediate or type 1 hypersensitivity is easily recognized because it involves quick and dramatic symptoms.
Hay fever is the most common expression of allergy and is a prototype of immediate hypersensitivity.
Hay fever is a reaction to airborne plant pollens in the nose. Allergy tests are positive, antihistamines help and allergy shots can reduce the reactivity over time. Delayed patterns of allergy are not so obvious and generally go unrecognized. Allergy skin tests do not show this problem nor do IgE antibody tests. By a practical evolution of allergy practice, those clinical problems which were diagnosable by skin reactions became the special property of allergists.