According to the Centers for Disease Control and Prevention (CDC), there are seven million children in the United States that are affected by asthma. Asthma costs the United States 56 billion dollars each year and is responsible for 3,388 deaths in 2009.

Many investigators have been researching the reason for why children who grow up on farms have lower allergy and asthma rates due to being continuously exposed to microorganisms in soil, compared to children from the inner-city, who are regularly exposed to roach and mouse allergens have increased asthma risks.

Published in the Journal Allergy and Clinical Immunology, scientists from the Johns Hopkins Children's Center in Baltimore, MD, performed a study with 467 inner-city newborns in Baltimore, MD, Boston, MA, New York, NY, and St. Louis, MO to find why inner-city children exposed to roach and mouse allergens increase the asthma risks. Monitoring their health over three years, the researchers visited the infants' homes to quantify the levels of allergens.

During those house visits, the researchers used blood exams, skin-prick tests, physical exams, and parental surveys to test the infants or allergies and wheezing.

The results suggested that infants who lived in homes with rodent and pet dander, as well as cockroach droppings during their first year, had lower wheezing rates at age 3, compared with children not exposed to such allergens. More specifically, infants who were not exposed to allergens were three times more likely to develop asthma and experience wheezing.

Also, the researchers found that children who lived in environments with an increased variety of bacteria were less likely to develop allergies by age three.

“Our study shows that the timing of initial exposure may be critical. 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,” says study author Dr. Robert Wood, chief of the Division of Allergy and Immunology at the Johns Hopkins Children's Center.