Children who were exposed to allergens and bacteria during infancy are less likely to suffer from allergies, according to a recent study.

Scientists at the Johns Hopkins Children's Center found that babies 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, Live Science reported. 

"Our study shows that the timing of initial exposure may be critical," Robert Wood, M.D., study author and chief of the Division of Allergy and Immunology at the Johns Hopkins Children's Center, said in a statement. "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."

For the study, researchers visited and tracked the homes of more than 450 inner-city newborns from Baltimore, Boston, New York and St. Louis for three years. They measured the levels and types of allergens present in the infants' surroundings and tested them for allergies and wheezing via periodic blood and skin-prick tests, physical exams and parental surveys.

Based on their findings, infants who grew up in homes 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. The protective effect, moreover, was additive, the researchers found, with infants exposed to all three allergens having lower risk than those exposed to one, two or none of the allergens.

Researchers said wheezing was three times as 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).

They concluded that infants in homes with a greater variety of bacteria were less likely to develop environmental allergies and wheezing at age 3.

The findings were recently published in the Journal of Allergy and Clinical Immunology.