infant crawling on the floor
June 7, 2014

Early Exposure To Allergens May Prevent Asthma, Allergies And Wheezing

Rebekah Eliason for - Your Universe Online

According to a new study from Johns Hopkins Children’s Center and other institutions, babies who are exposed to rodent and pet dander, roach allergens and household bacteria within their first year of life are less likely to experience allergies, wheezing and asthma.

Previous studies have demonstrated how children living on farms have lower rates of allergies and asthma. This phenomenon was attributed to the regular exposure to microorganisms found in farm dirt. In contrast, other studies have found children living in the city have increased asthma risk when exposed to high levels of roach and mouse allergens and pollutants.

Although this new study does confirm children living in houses with high allergy pollutants do have a higher overall allergy and asthma rate, they discovered when babies are exposed to allergens before their first birthday they actually benefit from the substances. However, if a child encountered the substances after the age of one, the protective effects of the exposure were not seen.

In a report about the study, authors hypothesized that early bacterial and allergen exposure may protect by shaping the immune response of the child. This discovery may help develop preventative treatments for allergies, wheezing and asthma.

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

Participants of the study were from Baltimore, Boston, New York and St. Louis and consisted of 467 inner-city newborns whose health was recorded for three years. Researchers conducted tests at each child’s home to measure the levels and types of allergens present in the infant’s daily surroundings. Also, the babies were tested for allergies using periodic blood and skin-prick tests, physical exams and parental surveys. Additionally, researchers took samples of dust and analyzed their bacteria content for 104 of the 467 homes.

When compared to children who were not exposed to mouse and cat dander and cockroach droppings, infants who grew up in a home with the allergenic pollutants experienced lower rates of wheezing at age three. Interestingly, it was found that the protective effect of exposure was additive. When infants were exposed to all three of the allergens, they had an even lower risk than those who were only exposed to one, two or none of them. Children who grew up with no exposure to the three allergens were three times more likely to experience wheezing than the children who were exposed within their first year of life.

Additionally, the wider the variety of bacteria in the home, the less likely infants were to develop wheezing by the age of three.

Interestingly, 41 percent of wheeze-free and allergy-free children grew up in the most allergen and bacteria-rich homes. In contrast, only eight percent of children who had both allergies and wheezing had been exposed to these substances within the first year of their life.

According to the US Centers for Disease Control and Prevention, in the United States, seven million children are affected by asthma. Half of all children develop wheezing by the age of three, which will often develop into full-blown asthma.

This study was published June 6 in the Journal of Allergy and Clinical Immunology.