Several studies have reported lower rates of allergic sensitization and allergies in children living in rural as compared to urban communities. This has been attributed to the lower levels of air pollution in rural areas. The question arises whether other factors in the rural environment could explain the lower prevalence rates of allergic sensitization and hay fever. A first report from rural South Bavaria in Germany demonstrated that children living in a home where coal and wood were used for heating had a significantly lower risk of suffering from hay fever (odds ratio 0.57 (0.34-0.98)), of being sensitized to common allergens (OR 0.67 (0.49-0.93)) and of having bronchial hyperresponsiveness (OR 0.55 (0.34-0.90)) than their peers living in homes with other heating systems. Subsequently, the Swiss Study on Childhood Allergy and Respiratory Symptoms with Respect to Air Pollution (SCARPOL) tested the hypothesis that farming as parental occupation was associated with a lower risk of hay fever and atopy. A total of 1620 (86.0%) 6-15-year-old schoolchildren living in three rural communities of Switzerland were examined using a standardized questionnaire completed by the parents and IgE antibodies against six common aeroallergens in serum samples of 404 (69.3.0%) of the 13-15-year-olds. Farming as parental occupation was significantly associated with lower rates of reported hay fever symptoms and allergic sensitization. Comparing children from farming with those from non-farming environments, the adjusted OR was 0.34 (95% CI: 0.12-0.89) for sneezing attacks during the pollen season, and 0.31 (95% CI: 0.13-0.73) for a sensitization to allergens. These results have recently been confirmed in a new and much larger survey in rural South Bavaria. Several alternative explanations have to be considered when interpreting these findings, namely, selection bias, the development of tolerance, increased microbial stimulation and a more traditional lifestyle (diet and housing conditions). Based on present knowledge, the underlying environmental factor explaining the protective effect of the farming environment has not yet been identified.