Though a parent's instinct may be to protect their newborn from things like household bacteria, dander and allergens, new research suggests infants who are exposed to these irritants during their first year of life are less likely to experience allergies, wheezing and asthma.

The research, led by scientists at the Johns Hopkins Children's Center in Baltimore, MD, publish their findings in the journal Allergy and Clinical Immunology.

According to the Centers for Disease Control and Prevention (CDC), 7 million children in the US are affected by asthma. A condition costing the US $56 billion each year, asthma caused 3,388 deaths in 2009.

While previous studies have shown that children who grow up on farms have lower allergy and asthma rates, due to being regularly exposed to microorganisms in soil, others have suggested inner-city-dwelling kids exposed to roach and mouse allergens have increased asthma risks.

To further investigate why this may be, the researchers conducted their study among 467 inner-city newborns in Baltimore, MD, Boston, MA, New York, NY, and St. Louis, MO. Tracking their health over 3 years, the researchers visited the infants' homes to measure levels of allergens.

The team tested the infants for allergies and wheezing by employing blood and skin-prick tests, physical exams and parental surveys. They also collected the bacterial content of dust from the homes of 104 of the 467 infants and analyzed it.

More allergen exposure resulted in greater protective effects

Results showed that, compared with children not exposed, infants who lived in homes with mouse and cat dander and cockroach droppings during their first year had lower wheezing rates at age 3.

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The new study reveals that infants who are exposed to allergens and bacteria during their first year of life are less likely to experience allergies, wheezing and asthma.

But interestingly, the more allergens the infants were exposed to, the greater the protective effect; infants exposed to all three allergens had a lower risk than those who were exposed to none, one or two of them.

In detail, children who grew up without being exposed to the allergens were three times as likely to experience wheezing, compared with those who grew up with all three allergens.

The team also observed that infants who lived in homes with a greater variety of bacteria were not as likely to develop environmental allergies and wheezing by age 3.

Their findings could help to inform preventive strategies for allergies and wheezing, say the researchers, which can both lead to asthma.

Commenting on their findings, study author Dr. Robert Wood, chief of the Division of Allergy and Immunology at the Johns Hopkins Children's Center, says:

"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."

Protective effects of exposure not valid after first year of life

An additional finding came about when the team analyzed the effects of cumulative exposure to both bacteria and mouse, cockroach and cat allergens.

They found that children who did not experience wheezing and allergies at age 3 were exposed to the highest levels of household allergens during their first year of life and were most likely to live in houses with the widest variety of bacterial species.

Of the children who were free of allergies and wheezing, 41% had grown up in these environments, whereas only 8% of children who experienced both allergies and wheezing were exposed to these toxins during their first year.

Though their findings are significant, the researchers say the protective effects of exposure to these substances were not observed if the child's first experience with them occurred after the age of 1.

Medical News Today recently wrote a feature debunking the myth that asthma is a minor condition.