The prevalence of
asthma and allergic disease has increased worldwide over the last few decades. Many common environmental factors are associated with this increase. Several theories have been proposed to account for this trend, especially those concerning the impact of environmental toxicants. The development of the immune system, particularly in the prenatal period, has far-reaching consequences for health during early childhood, and throughout adult life. One underlying mechanism for the increased levels of allergic responses, secondary to exposure, appears to be an imbalance in the T-helper function caused by exposure to the toxicants. Exposure to environmental
endocrine-disrupting chemicals can result in dramatic changes in
cytokine production, the activity of the immune system, the overall Th1 and Th2 balance, and in mediators of type 1
hypersensitivity mediators, such as
IgE. Passive exposure to tobacco
smoke is a common risk factor for
wheezing and
asthma in children. People living in urban areas and close to roads with a high volume of traffic, and high levels of
diesel exhaust fumes, have the highest exposure to environmental compounds, and these people are strongly linked with type 1
hypersensitivity disorders and enhanced Th2 responses. These data are consistent with epidemiological research that has consistently detected increased incidences of
allergies and
asthma in people living in these locations. During recent decades more than 100,000 new chemicals have been used in common consumer products and are released into the everyday environment. Therefore, in this review, we discuss the environmental effects on
allergies of indoor and outside exposure.