Explore this issue:March 2013
Allergies have been on the rise in industrialized countries for more than 50 years, according to statistics collected by the American Academy of Allergy, Asthma and Immunology. In the United States, approximately 10 percent of children suffer from hay fever and 8 percent from a food allergy of some kind. The U.S. Centers for Disease Control and Prevention documented an 18 percent increase in the number of youngsters who reported a food allergy between 1997 and 2007.
Allergies can cause a variety of ear, nose, throat and sinus issues and many otolaryngology practices offer allergy-related services, including a majority of academic otolaryngology departments in the U.S.
Allergies tend to run in families, but genetics cannot explain the rise in cases. So scientists, epidemiologists and physicians have looked to environmental influences, especially those found in first-world countries and, increasingly, in urban settings. A study published in September 2012, which surveyed U.S. households and analyzed data for 38,465 children, found higher rates of food allergy in urban areas (9.8 percent) versus rural areas (6.2 percent) (Clinical Pediatrics. 2012;51:856-861).
The “hygiene hypothesis” provides a popular framework for thinking about early environmental exposures and the development of allergic sensitization. Essentially, the hypothesis is that modern society offers a cleaner environment for kids to grow up in than did our mostly agrarian past, one free of many microbes and infections that used to go hand-in-hand with childhood and that, as the theory goes, primed the immune system to recognize true threats and ignore innocuous ones such as ragweed pollen or peanut antigens.
At the same time, present-day city life exposes children to a slew of things that were not a part of growing up just a few generations ago. To that end, researchers have started looking at environmental pollutants as possible triggers of allergic sensitization. Second-hand smoke tops the list, but recent studies have indicated that the chlorine in pools, pesticides and certain air pollutants are also associated with a greater risk for allergies (Semin Immunopathol. 2012;34:655-669.).