From the U.S.Library of Medicine National Institutes of Health.
The prevalence of asthma and other atopic diseases has recently increased, especially in urban and modernized regions of the world. The majority of published prevalence surveys report that asthma and atopy are less common among children living in rural areas. While many exposures differ in rural and urban areas of the world, several recent studies have suggested that agricultural exposures in early childhood may decrease the risk of developing atopic disease. Livestock exposure, in particular, seems to be important, but additional research is needed to pinpoint the underlying mechanisms behind this apparent protective effect of rural and farm living. Additionally, prospective studies are needed to more closely examine the timing of farm exposures in relation to the onset of asthma and atopy, and to determine if the apparent protective effects of farming persist into adulthood.