When this antibody meets an allergen, histamine-like substances are produced. It is these substances that cause allergic symptoms. The answer is that some people are born with an inherited susceptibility to allergy, manifested by a tendency to make excessive amounts of IgE antibodies. Allergy is not rare. Close to one-fifth of the people living in the United States have an allergy.
Hay fever is the most common allergy, followed by asthma.
What the child becomes allergic to will depend on what allergens the child is exposed to. Food allergies are not as common as hay fever. The incidence of food allergy ranges from 1 percent to 15 percent, depending on how it is defined. However, food allergies can be very serious. In a study of children with anaphylaxis, the most severe of allergic manifestations that can result in respiratory and cardiac collapse, foods were the second most common cause, responsible for a fourth of the cases.