RT Book, Section A1 Chatila, Talal A. A2 Rudolph, Colin D. A2 Rudolph, Abraham M. A2 Lister, George E. A2 First, Lewis R. A2 Gershon, Anne A. SR Print(0) ID 7018499 T1 Chapter 190. Allergic Disease and Atopy T2 Rudolph's Pediatrics, 22e YR 2011 FD 2011 PB The McGraw-Hill Companies PP New York, NY SN 978-0-07-149723-7 LK accesspediatrics.mhmedical.com/content.aspx?aid=7018499 RD 2024/03/28 AB A precipitous increase in incidence and prevalence of allergic diseases in the last decades leads to the current estimate that up to 50% of the population of Western societies shows reactivity on skin testing to one or more environmental allergens.1 In some subpopulations, up to one in four children suffer from asthma. One explanation for this dramatic increase in allergic diseases is the “hygiene hypothesis,” which posits that a decrease in the exposure to microbes due to improved hygiene, smaller families, less breastfeeding, more immunizations, and lack of serious childhood infections results in altered immunoregulation and deviation toward an allergic disease-promoting TH2 response. Microbial exposure promotes the production of regulatory T cells involved in maintaining tolerance to allergens (see Chapter 186). Lack of sufficient microbial exposure may result in weakened tolerance and, in the setting of other factors such as genetic predisposition and environmental exposures, result in the promotion of allergic diseases.