A marked increase in allergic diseases has been linked to the hygiene environment in early infancy. Infants exposed to more children at home or day-care experienced less frequent wheeze from year 8 through year 13 and were less likely to have elevated serum IgE levels.6–
Improved hygiene in industrialized societies and the use of vaccine and antibiotics have been reported to reduced the incidence of infections that would normally stimulate the immune system in some way that mitigates against asthma.7–
Whether exposure to endotoxin (lipopolysaccharide), a potent inducer of interleukin-12 and interferon-γ, is protective or harmful is likely to depend on a complex mixture of timing of exposure during the life cycle, environmental cofactors, and genetics. In both animal models and studies in humans, exposure to endotoxin early in life, during the development of the immune system, seems to be most important in providing protection against the development of allergic disease.8
For older children, the use of antibiotics should not bring about increased allergic diseases.