New research lends support to the idea that exposure to a wide range of microbes explains why farm kids have lower asthma rates than city kids.
School-aged children in the studies who lived on farms were about 30% to 50% less likely to have asthma than non-farm children who lived nearby.
Farm-dwelling children were also exposed to more bacteria and fungi than the other children.
The studies, which appear in the Feb. 24 edition of the New England Journal of Medicine, suggest a role for the so-called hygiene hypothesis in the development of childhood asthma.
According to the hypothesis, exposure to bacteria and fungi from environmental sources like dirt and animal hair early in life protects against asthma and allergies by helping the immune system develop normally.
It is theorized that increasingly clean environments may at least partially explain why asthma rates have doubled in developed nations in just the last three decades.