Sometimes psychic factors, stemming from emotional conflicts, play an important role in allergy. The mechanism of allergic reactions is not fully understood. Most likely the antigen becomes localized in a particular tissue, such as the cells lining the nasal passages or the bronchial tubes. The antibody reacts with the antigen at these sites, causing the release of certain chemical substances, including histamine, which mediates, or brings about, the reaction. Sometimes testing the skin with a wide variety of common allergens can pinpoint the specific allergen or allergens that are causing the difficulties.
The simplest and best treatment is, when possible, to avoid contact with the allergen. A person allergic to feathers, particular pollens, foods, or medicines, for example, should avoid them. Where this is not feasible, because the allergen is unknown, because it affects more than one part of the body, or because too many allergens are present, drugs such as antihistamines or, in more serious cases, adrenal cortical steroids may be used to decrease the reaction. In other cases desensitization (the process of making the patient able to tolerate the antigen without having a reaction) may be accomplished by giving injections of antigen, first in minute doses and then in gradually increasing doses as tolerance builds up. Skin testing is always needed when desensitization treatment is being considered. Symptomatic treatment, such as the administration of drugs to relax spasms in the walls of the bronchi in asthmatics, decongestants for hay fever sufferers, or local ointments to relieve itching for hives may also be useful.