Oct. 31, 2014

By Medical Discovery News

Common knowledge and previous studies generally agree that children who grow up in the inner city and are exposed to mouse allergens, roach allergens, and air pollutants are more likely to develop asthma and allergies. But a recent study adds a new twist – children exposed to these substances in their first year of life actually had lower rates of asthma and allergies. However, if these allergens were first encountered after age one, this protective effect did not exist.

Another study parallels this one, concluding that children growing up on farms also have lower allergy and asthma rates. Scientists argue that farm children are regularly exposed to microbes and allergens at an early age, leading to this same protective effect.

Asthma is the most common chronic condition among children. One in five Americans, or 60 million people, has asthma and allergies. In the industrialized world, allergic diseases have been on the rise for more than 50 years. Worldwide, 40-50 percent of school-age children are sensitive to one or more common allergens.

In this study, scientists enrolled 467 children from the inner cities of Baltimore, Boston, New York City, and St. Louis and followed their health since birth. The infants were tested for allergies and wheezing by periodic blood tests, skin-prick tests, and physical exams, and their parents were surveyed. They also sampled and analyzed the allergens and dust in the homes of over 100 of the subjects.

Children who lived in home environments that included cat and mouse dander as well as cockroach droppings in their first year of life were much less likely to develop wheezing or allergies when compared to children who were not exposed to these substances. This protective effect was additive, so children exposed to all three were less likely to develop wheezing compared to children exposed to two, and those children were more protected than those who were exposed to only one. Only 17 percent of children who lived in homes with all three allergens experienced wheezing by age three, compared to 51 percent of children who lived in homes without such allergens. Interestingly, dog dander did not have a protective effect against the development of allergies or wheezing.

The richness of the bacterial populations children were exposed to enhanced this protective effect. This suggests that household pests may be the source of some of the beneficial bacteria in the inner city environment. Early exposure to allergens and certain bacteria together provide the greatest effect.

An infant’s microbiome, the total makeup of bacteria in and on their bodies, is developed during their first year of life. The bacteria colonizing an infant’s gastrointestinal system affects their immune system and influences the development of allergies. Scientists hypothesize that something similar may be happening in the airways and lungs, as kids with asthma have altered bacterial populations in their respiratory systems.

There is mounting evidence exposures to allergens and bacteria in the first few months of life help shape the respiratory health of children. But we don’t yet know how specific allergens and bacteria induce this protective effect, or how they can be used to treat children and reduce their chances of developing allergies and asthma.

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