Babies crawling to chase after bugs or the family pet are off to a healthy start. According to a new study, babies who are exposed to household dirt, pollen, and pet dander have a lower risk of developing asthma or allergies.

The study published June 6 in the Journal of Allergy and Clinical Immunology found that before their first birthday, babies who are exposed to allergens have a lower risk of developing both allergies or breathing problems, such as wheezing or asthma. Researchers from the Johns Hopkins Children’s Center found that bacteria and allergens have a protective effect on young children’s immune systems, that ward of these illnesses in the future. However, those young ones who were exposed to these allergens past their first birthday did not get the same healthy effects.

“Our study shows that the timing of initial exposure may be critical,” said study author and chief of the Division of Allergy and Immunology at the Johns Hopkins Children’s Center, Robert Wood, M.D. stated in a news release. “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 researchers tracked the health 467 newborns from Baltimore, Boston, New York, and St. Louis over the course of three years. They tested what allergens where in their homes and surroundings, as well as taking blood and skin tests, physical exams, and parental surveys to test for allergies and wheezing.

Although this might make a New York parent happy to see a roach in their apartment, the study found that babies living in homes with mouse and cat dander, and cockroach droppings had a lower rate of wheezing by age three, compared to those children not exposed. Furthermore, those babies exposed to all three allergens had a lower risk than those exposed to just one.

41% of children who were allergy and wheeze-free had grown up in homes with allergens and bacteria. Only 8% who suffered from both had been exposed during their first year.

Previous research has found that children who live on farms have lower allergy and asthma rates compared to their city-dwelling counterparts. This is because they are regularly exposed to microorganisms in the farm soil.

According to the Centers for Disease Control and Prevention, 7 million American children suffer form asthma.

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