A combination of genetic and environmental factors causes allergies in children. Genetics play a powerful role in determining a child’s predisposition to allergies. According to the Asthma and Allergy Foundation of America (AAFA), a child has about a 50 percent chance of developing allergies if one parent is allergic. The odds jump to 75 percent when both parents have allergies. However, parents and children do not necessarily share the same allergies, and some children with highly allergic parents remain symptom-free.

While genetics may predispose a child towards allergies, it is environmental factors that trigger the allergy itself. An allergic reaction cannot occur the first time a child is exposed to a potential allergen – instead, there must be a period of sensitization where the immune system produces its initial antibodies to the antigen. Once this process takes place, an allergic reaction is primed to occur the next time the child is exposed to the allergen.

Environmental factors also are at the root of a theory that seeks to explain why more children suffer from allergies and asthma today than in the past. A growing body of evidence supports the notion that childhood allergies and asthma have increased as society has placed a greater emphasis on cleanliness.

According to the so-called “hygiene hypothesis,” today’s children are too insulated from bacteria and other agents that cause infections. This has retarded the development of their immune systems, putting them at greater risk for becoming allergic or asthmatic, according to the theory.  However, this theory remains in dispute and research is ongoing.