Writing in the June, 2014, edition of the Journal of Allergy and Clinical Immunology, researchers “sought to examine environmental factors associated with recurrent wheezing in inner-city environments. The Urban Environment and Childhood Asthma study examined a birth cohort at high risk for asthma (n = 560) in Baltimore, Boston, New York, and St Louis. Environmental assessments included allergen exposure and, in a nested case-control study of 104 children, the bacterial content of house dust collected in the first year of life. Associations were determined among environmental factors, aeroallergen sensitization, and recurrent wheezing at age 3 years.” As summarized by John Hopkins Medicine, the study found that “infants exposed to rodent and pet dander, roach allergens and a wide variety of household bacteria in the first year of life appear less likely to suffer from allergies, wheezing and asthma….Previous research has shown that children who grow up on farms have lower allergy and asthma rates, a phenomenon attributed to their regular exposure to microorganisms present in farm soil. Other studies, however, have found increased asthma risk among inner-city dwellers exposed to high levels of roach and mouse allergens and pollutants. The new study confirms that children who live in such homes do have higher overall allergy and asthma rates but adds a surprising twist: those who encounter such substances before their first birthdays seem to benefit rather than suffer from them. Importantly, the protective effects of both allergen and bacterial exposure were not seen if a child’s first encounter with these substances occurred after age 1, the research found….‘Our study shows that the timing of initial exposure may be critical,’ says study author Robert Wood, M.D., chief of the Division of Allergy and Immunology at the Johns Hopkins Children’s Center. ‘What this tells us is that not only are many of our immune responses shaped in the first year of life, but also that certain bacteria and allergens play an important role in stimulating and training the immune system to behave a certain way.’”

The study’s abstract and report from John Hopkins Medicine are both online, as is an article in USA Today.