What exactly is in Amish house dust that might protect children is not known and more research is planned to find out, but the study authors theorized it could be microbes including bacteria from dairy cows.



"We could just say put a cow in everyone's house and no one would have asthma anymore, but of course, that's not easy," Ober said with a chuckle.



But if protective germs can be identified, it might someday be possible to create an asthma blocker for all children, she said.



A journal editorial said the study bolsters evidence that exposure to germs from traditional farming may protect against asthma. The results also support the so-called "hygiene hypothesis," which theorizes that relatively germ-free homes of modern society make infants more vulnerable to allergies and asthma.



Dr. Talal Chatila, an allergy expert at Boston Children's Hospital who wrote the editorial, said the study doesn't answer when and how often exposure to farm dust might be needed to protect children and if it needs to begin before birth.



Ober noted that research has shown that infants whose families have dogs are less likely to develop asthma and allergies but that acquiring a dog later on doesn't make a difference.



Associated Press