KIDS
June 11, 2014

Infant Immunity

When it comes to allergens and bacteria, early exposure may be better than no exposure, a finding that surprised researchers and should ease parents' minds.

A recent study revealed some surprising information about why some young children are prone to wheezing illnesses and asthma, while others appear to escape this common childhood malady.

Early exposure to allergens has been associated with wheezing illnesses in inner city children. Children who live on farms and are exposed to environmental microorganisms early in life have lower rates of allergy and asthma than their urban counterparts. What is the difference?

Timing is key in allowing the new immune system to develop helpful defenses against environmental allergens.

Researchers suspected the types of allergens and microbes children are exposed to in early childhood might play a role. They tracked the environmental exposures and the health of 467 inner city infants in four cities over a three-year time period.

They measured the types and levels of allergens (such as rodent and pet dander and roach allergens) in their homes and tested the children for signs and symptoms of allergies. The types of bacteria present in 104 of the study homes were also identified and measured.

Children who had the greatest cumulative exposure to allergens during the first three years of life showed the greatest increase in allergic sensitization and wheezing, a finding consistent with many previous studies.

What was surprising, however, was that children who had the highest exposure to pet dander and cockroach allergens during their first year of life had the least recurrent wheezing compared to those whose exposure was higher later.

The higher the first year of life exposure, the lower the risk of allergic symptoms, but this inverse relationship was not observed after the first year of life.

The researchers concluded that timing is key in allowing the new immune system to develop helpful defenses against environmental allergens, and once the first year has passed the immune system no longer reacts protectively. Instead, it triggers allergic and wheezing symptoms when the allergens are encountered again.

Children whose environments were rich in certain types of bacteria, along with the allergens, also had less wheezing/allergies than their peers. This protective effect was most apparent in the children exposed highly in the first year of life as well.

Dirt rich in bacteria and animal dander was found in homes of 41% infants who made it to age 3 without allergies or wheezing, as opposed to only 7% of those who did not.

This may be a similar effect to the bacteria-rich environment in which farm children are raised that primes the immune system against allergens and protects children from allergic reactions to environmental pollutants, the researchers believe.

Parents are not encouraged to surround their young children with allergens, dirt and bacteria, but they should feel less compulsive about aiming for a sterile environment for their young children.

The investigators speculate that early exposure, especially to both allergens and certain microbes, might impact the immune tissues located in the gut and lungs and lead to the decreased allergic symptoms in later childhood.

It's too early to offer clinical applications for the findings, but the researchers hope that they will lead to improved strategies for decreasing the burden of wheezing and allergic disease on young children.

Parents are not encouraged to surround their young children with allergens, dirt and bacteria, but they should feel less compulsive about aiming for a sterile environment for their young children. Talk with your children’s health care providers about appropriate pets and hygiene practices if you have newborns and young children.

When it is known that a child is sensitive to environmental allergens such as pet dander or roach droppings, the family should try to minimize ongoing exposure.

The study is published in The Journal of Allergy and Clinical Immunology.

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