Not until 1915 did bronchial asthma, hay fever, urticaria and certain forms of eczema or inflammation of the skin come to be called allergic disorders. At that time the idea of sensitization and reaction of the body to certain foreign substances was established as a reality. Later other conditions such as serum sickness, reactions to drugs, and some blood vessel disturbances were added to the list.
Allergy today is conceived to be the results of contact of a foreign substance with its specific antibody in the human system. Repeated exposure to the foreign substance or allergen sets up the excess sensitivity.
Experts distinguish certain allergic disorders as atopic-meaning a strange disease-because they are largely hereditary, because the allergens which set them up are nontoxic substances like pollens or foods, and because the first manifestation is a swelling with accumulation of water in the tissues. The diagnosis of the condition is made by putting the allergen on the skin, whereupon a blister or wheal forms. This accumulation of fluid is due to the release of a substance called histamine. As a part of our progress we have developed antihistaminic drugs. If these are given before making the skin tests, the wheals do not develop.
The majority of people who develop atopic conditions do so before they are twenty years old. The real allergic conditions appear usually after the person affected is thirty years of age or older. Dr. Harry Alexander points out that a child who becomes subject to asthma at the age of five almost surely is hypersensitive to a specific allergen which it inhales or swallows.
Because of the reactions that occur in the skin the use of tests for determining the nature of allergic conditions is standard.