Early exposure to common allergens builds immunity

Scientists offer new insights to an old idiom

The old adage “you have to eat a peck of dirt before you die” is often used to comfort horrified mothers who catch their first-born playing in situations that are — ahem — less than clean.

But researchers now say children who are exposed to dirt, dander and germs — specifically in their first year of life — tend to have fewer allergies and asthma later.

In fact, infants exposed to rodent and pet dander, roach allergens and a wide variety of household bacteria in the first year of life appeared less likely to suffer from allergies, wheezing and asthma, according to results of a study conducted by scientists at the Johns Hopkins Children’s Center and other institutions.

Previous research has shown that children who grow up on farms have lower allergy and asthma rates, a phenomenon attributed to their regular exposure to micro-organisms present in farm soil.

Cockroaches, pet dander as immunity boosters?

Cockroaches, pet dander as immunity boosters?
photo: Thinkstock

Other studies, however, have found increased asthma risk among inner-city dwellers exposed to high levels of roach and mouse allergens and pollutants. The new study confirms that children who live in such homes do have higher overall allergy and asthma rates, but adds a surprising twist: Those who encounter such substances before their first birthdays seem to benefit rather than suffer from them. Importantly, the protective effects of both allergen and bacterial exposure were not seen if a child’s first encounter with these substances occurred after age one, the research found.

A report on the study, published on June 6 in the Journal of Allergy and Clinical Immunology, reveals that early exposure to bacteria and certain allergens may have a protective effect by shaping children’s immune responses — a finding that researchers say may help inform preventive strategies for allergies and wheezing, both precursors to 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.”

Asthma is one of the most common pediatric illnesses. By the time they turn three, up to half of all children develop wheezing, which in many cases evolves into full-blown asthma. But scientists now say strict avoidance of allergens to avoid asthma risk has proven unsuccessful.

“If confirmed by other studies, these findings might even have us think of returning to the patterns of exposure of the 1940s, when families were larger, food was less processed and sterilized, and children spent a lot of their time outdoors,” said co-researcher UCSF pulmonologist Dr. Homer Boushey.

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