The findings suggested that children who were exposed to higher concentrations of cockroach, mouse and cat allergens during the first three years of life were linked to a lower risk of developing asthma -- that intermittently inflames and narrows the airways -- by 7 years of age.
A similar association was found for dog allergens, the researchers observed.
"Our observations imply that exposure to a broad variety of indoor allergens, bacteria and bacterial products early in life may reduce the risk of developing asthma," said James E. Gern, Professor at the University of Wisconsin-Madison in the US.
In addition, microbial environment in the home during infancy may be also be associated with reduced risk of asthma, the researchers noted in a paper published in the Journal of Allergy and Clinical Immunology.
Previous study suggested that exposure to certain bacteria during infancy may protect three-year-olds from recurrent wheezing, a risk factor for developing asthma.
However, additional research is needed to clarify the potential roles of these microbial exposures in asthma development, the researchers noted.
"We are learning more and more about how the early-life environment can influence the development of certain health conditions," said Anthony S. Fauci, Director at the National Institute of Allergy and Infectious Diseases (NIAID) in Maryland.
"If we can develop strategies to prevent asthma before it begins, we will help alleviate the burden this disease places on millions of people, as well as on their families and communities," Fauci added.
For the study, the team investigated risk factors for asthma among 442 children living in urban areas, where the disease is more prevalent and severe.
Among these 130 children (29 percent) developed asthma through 7 years of age.