Prevention. There is some evidence that children who were breast-fed have fewer type I and type IV hypersensitivities. It is also thought that too restricted and "hygienic" an environment may play a role in increasing allergies. Some studies have shown that infants raised on farms tend to have fewer allergies than those raised in a more allergen-free environment.
Avoidance and Elimination. Once an allergy has developed, the best way to prevent a reaction is to prevent exposure wherever possible. In the case of food, this may mean a lifetime elimination of that substance from the diet and vigilance in watching for hidden ingredients in processed and restaurant food. For example, a spatula that has touched peanut butter cookies before touching chocolate chip cookies may be contaminated enough to provoke a reaction in a peanut-sensitive person.
In the case of insects and animals, avoidance is best. In the case of airborne pollens, such as regional weeds and grasses, limiting time outside can help but may not prevent the problem. Some people try moving to another area to avoid certain local allergens; this may not be effective since people with allergies often develop new allergies to pollens or grasses in the region to which they move.
Desensitization (immunotherapy, specific immune therapy, "allergy shots") is sometimes recommended if the allergen cannot be avoided. It includes regular injections of the allergen, given in increasing doses that may "acclimatize" the body to the allergen. The shots decrease the amount of IgE antibodies in the blood and cause the body to make a protective antibody, another of the immunoglobulins, IgG. Because it moves across the placental barrier, IgG is important in producing immunity in an infant before birth. Immunotherapy shots can cause side effects, like hives and rashes, and can trigger anaphylaxis. Desensitization is most effective for those with hay fever symptoms and severe insect sting allergies. Many with hay fever may have a significant reduction in their symptoms within 12 months, and it is effective in about two-thirds of those who try it. People may continue their shots for 3 years, then consider stopping. Some will have long-term relief; others will see a resumption of their symptoms. Immunotherapy is not recommended for food allergens.
Short-term symptomatic treatment is used for the relief of symptoms. For example, with respiratory symptoms, treatment may include antihistamines, topical nasal steroids, oral steroids, or decongestants.
In the case of anaphylaxis, epinephrine injections are required. Those who have severe reactions must carry a kit that contains an emergency injection of epinephrine with them at all times. Anyone who has a reaction and uses epinephrine should seek medical treatment, as follow-up treatment is often needed.