Environmental factors as a cause for the increase in allergic disease.

LEARNING
OBJECTIVES: To be able to understand the interaction among genetic factors, environmental exposure to allergens, and nonspecific adjuvant factors contributing to the increase in atopic diseases in developed countries. DATA SOURCES: Peer-reviewed literature identified by searching medical databases. STUDY SELECTION: Careful review of epidemiologic cross-sectional, sequential, and longitudinal population studies and, when appropriate, intervention studies. The criteria used to accept a study reporting environmental factors influencing the prevalence of allergic diseases were adopted from the report published by the US Department of Health and Education in 1964 (Hill AB, Principles of Medical Statistics, 9th Ed. New York: Oxford University Press, 1971, p. 323)
RESULTS: There is ample evidence that specific environmental factors may cause sensitization and development of allergic symptoms and disease in susceptible individuals. It is unclear when and how long a sufficient exposure will result in clinical symptoms related to the immunoglobulin E-sensitizing agents.
CONCLUSIONS: Environmental factors play an important role for the development and manifestation of allergic conditions in genetically predisposed subjects. It is well documented that increased exposure to indoor allergens and selected outdoor allergens (eg, grass pollen and molds) and smoking are important risk factors for development of asthma and allergic sensitization. The importance of other environmental factors is less clear and which environmental factors that cause the increase in prevalence of allergic disease is still unknown.