Allergies are the most common chronic illness. Allergies are a disorder of the immune system. An allergy is described as an inappropriate response to a normally harmless invader. The concept of allergies is relatively modern with the first description appearing a little over a hundred years ago. Allergy rates vary across the world ranging from 10 to 40 percent of the population. Interestingly the richer the country is the more allergies the population has.
The increase in the number of individuals with allergies, particularly in richer countries, is not clearly understood. Lifestyle, diet choices and genetics all seem to play a role. In the United States about one person in five have allergies. If one parent has allergies, there is a 25 percent chance that a child will also be allergic. The risk of having an allergic child is 60 to 70 percent if both parents have allergies. Babies born in developing countries have a lower incidence of allergies than those in developed countries. However if a family moves to a developed country, the incidence of childhood allergies increases.