Abstract: The present invention relates to the asthma-protective effects of farm dust, specifically to a composition comprising barn dust extract including isolated fractions of an Amish barn dust extract comprising different bioactive components that have an ability to protect against asthma. In particular, the present invention describes a barn dust composition with asthma-protective properties, the barn dust composition comprising one or more bioactive fractions extracted from barn dust, said one or more bioactive fractions comprising one or more proteins and one or more fatty acids. The one or more bioactive fractions of the barn dust compositions may comprise molecular weights of 30-100 kDa, particularly 28-64 kDA, that include eight (8) target proteins, which have potential to proactively prevent the induction of asthma and to treat current cases of asthma. The present invention also relates to an in vitro method for screening allergic compounds.