Infants exposed to more “real” conditions tend to be healthier than those overly protected. A new study has shown that newborns 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. If the child has his/her first encounter with them after 1 year of life, he/she will have an increased risk of suffering from the above mentioned problems.

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Previous studies have already shown that children who grow up on farms and in rural areas tend to have lower rates of allergy and asthma, and this phenomenon has been attributed to the exposure to microorganisms in the soil. However, other studies have found increased rates of inner-city dwellers exposed to high levels of roach and mouse allergens and pollutants. This study confirms both those findings, and gives them an extra twist: those who encounter these substances before 1 year of age seem to benefit rather than suffer from them. Importantly, the protective effects of exposure to allergens and dust faded after 1 year of age.

“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 was conducted on 467 inner-city newborns from Baltimore, Boston, New York and St. Louis whose health was tracked over three years. They also analyzed the bacterial and dust content from their homes. Infants who grew up in houses with mouse and cat dander and cockroach droppings in the first year of life had lower rates of wheezing at age 3, compared with children not exposed to these allergens soon after birth. Furthermore, the effects were additive: children who were exposed to two or more types of allergens had reduced rates of risk than those who were exposed to just one.

Specifically, wheezing was 3 times more common among children who grew up without exposure to such allergens (51 percent), compared with children who spent their first year of life in houses where all three allergens were present (17 percent).

Journal Reference: Susan V. Lynch, Robert A. Wood, Homer Boushey, Leonard B. Bacharier, Gordon R. Bloomberg, Meyer Kattan, George T. O’Connor, Megan T. Sandel, Agustin Calatroni, Elizabeth Matsui, Christine C. Johnson, Henry Lynn, Cynthia M. Visness, Katy F. Jaffee, Peter J. Gergen, Diane R. Gold, Rosalind J. Wright, Kei Fujimura, Marcus Rauch, William W. Busse, James E. Gern. Effects of early-life exposure to allergens and bacteria on recurrent wheeze and atopy in urban children. Journal of Allergy and Clinical Immunology, 2014; DOI: 10.1016/j.jaci.2014.04.018