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Why Are Allergies on the Rise?

Research shows that allergies are on the rise. For instance, the number of people in the U.S. with hay fever (allergic rhinitis) increased by 31 percent between 1985 and 1995 and rose by another third between 2001 and 2005. In addition, the number of children in the U.S. with peanut allergies doubled between 1997 and 2002 and the number of kids in this country who are allergic to other foods such as milk and fish is also rising rapidly.
According to Dr. Sami L. Bahna, a professor of pediatrics and medicine and chief of allergy and immunology at Louisiana State University Health Sciences Center, "Food allergies aren't the only allergies on the rise---all the allergies are increasing." But why is this happening? The two most popular theories are the allergen exposure hypothesis and hygiene hypothesis.

  1. Allergen Exposure Hypothesis

    • The more you are exposed to an allergen the more likely you will become allergic to it. This can be seen in the increasing instances of allergies in urban environments of developed countries in which people spend increasing amounts of time indoors, where pet dander and dust mites abound.

    Allergen Exposure Early in Life

    • An adjunct to the allergen exposure hypothesis is that early childhood exposure to allergens increases the risk that the child will develop allergies and even asthma by the age of 11, though one study showed that this was not true for cat dander.

    Hygiene Hypothesis

    • Some medical health professionals believe the increase in allergies has occurred because people in industrialized countries are living in more sterile environments, where they have not been exposed to viruses, bacterial fungi and parasites that would help their immune systems develop the way they should. Since we don't have to fight off as many infections the body doesn't build up the necessary immunities. "When there is some degree of unhygienic conditions, the immune system from infancy adapts and develops to fight infection," Bahna says. "Cleanliness, antibiotics, whether they are needed or not, and vaccinations are allowing the immune system to develop as if 'I don't need you.' "

    Infections Early in Life

    • The theory is backed by studies that show that children who have infections early in life are less likely to experience allergic reactions later. Cultures in which children suffer from parasitic infections have fewer instances of adult hay fever and asthma, and those who have had the measles also have fewer allergies as they age. Nonetheless, the hygiene theory does not explain the high number of allergies in poor inner-city populations that have had increased exposure to allergens.

    The Jury Is Still Out

    • Some believe genes play a role in the occurrence of allergies. There are studies that indicate that the genes you inherit from your parents may predispose you to being allergic, though until more studies are conducted it is difficult to draw further conclusions.

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