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Newborns exposed to certain allergens, bacteria had lower risk for allergy, asthma
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Children in urban environments who had the highest exposure to specific allergens and bacteria in their first year had the least likelihood to have recurrent wheeze or allergic sensitization, according to recent study results.
“Our study shows that the timing of initial exposure may be critical,” researcher Robert A. Wood, MD, FAAAAI, director of allergy and immunology at the Johns Hopkins Children’s Center, said in a press release. “What this tells us is not only that many of our immune responses are 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.”
Robert A. Wood
Researchers examined a birth cohort of 560 children at high risk for asthma in four US urban areas. Allergen exposure was assessed, and the bacterial content of house dust collected in the first year of life was measured in a nested case control study of 104 children.
“Cumulative allergen exposure over the first 3 years was associated with allergic sensitization, and sensitization at age 3 years was related to recurrent wheeze,” the researchers said.
There was a negative association between recurrent wheeze and first-year exposure to cockroach (OR=0.6; 95% CI, 0.45-0.8), mouse (OR=0.65; 95% CI, 0.52-0.82) and cat allergens (OR=0.75; 95% CI, 0.61-0.92). Atopy and atopic wheeze were associated with the difference in house dust bacterial content in the first year. Children without atopy or wheeze were more likely to have exposure to high levels of both allergens and this subset of bacteria in the first year of life.
“High levels of cockroach, mouse, and to a lesser extent, cat allergen in the first-year inner-city house dust samples had a strong inverse relationship with recurrent wheeze at age 3 years,” the researchers reported. “This association was strongest for allergen levels in the first-year dust samples, suggesting that the first few months of life is a critical time period in childhood allergic disease development.”
“These results, especially those related to certain microbial exposures, do support the hygiene hypothesis,” Wood said in a separate release. “This is important since it has been said that the high rates of asthma and allergy in children living in inner cities presented an exception to hygiene hypothesis.”
Disclosure: See the study for a full list of relevant disclosures.
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Clifford W. Bassett, MD, FAAAAI, FACAAI
Does early life exposure to allergens, dirt and germs actually reduce the risk of developing asthma and related allergic conditions in young children?
That is the question that was posed by a recent study that sought to confirm whether the “hygiene hypothesis” is alive and well and likely a plausible explanation that may bring in newer strategies to reduce the risk of developing asthma and allergic diseases among young children.
The study authors report that in inner-city environments, those young children with the highest exposure to bacteria and common indoor allergens, such as cat and/or dog dander, as well as cockroach and mouse allergens were actually less likely to suffer from wheezing and develop allergic sensitization.
In fact those infants that were raised in homes with greater amounts of bacteria and various indoor allergens had less wheezing at age 3. They felt their findings represent another important study that embraces the “hygiene hypothesis” is real and may reflect a need for more real world practical preventive solutions for those children, especially with an increased risk for allergic diseases and or asthma.
Finally, it appears that the timing of the early exposure to specific indoor allergens and bacteria, at or before the first birthday, may actually be pivotal in whether a protective anti-allergy/asthma effect can be created.
Here is my take on all of this. It may come to be that creating an oversanitized home environment will be counterproductive in developing a healthier immune system among very young children. Yes, that does mean having early exposure to lots of pets and perhaps a not-so-squeaky-clean home environment will actually be beneficial in reducing the prevalence of asthma and related allergies.
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Mark Holbreich, MD, FAAAAI
The work of Dr. Wood and his colleagues is of great interest. The hygiene hypothesis is a theory that exposure to microbes early in life is protective against the development of allergies and asthma. This hypothesis seems to be supported by studies showing that children who grow up on “traditional” farms have fewer allergies than children who grow up in a nonfarm environment. Traditional farms exist in Europe and among the Amish community in American. Life on these farms seems to protect children through early exposures in the barn to a rich microbial environment, large animals, as well as drinking raw milk.
Inner-city life in America has always been thought to be the source of a high prevalence of allergies and asthma. In Dr. Wood’s study they did in fact find this; however, in one cohort who had high microbial exposures as well as exposure to cats, cockroach and mouse, there was a significant reduction in the prevalence of allergies and asthma. Children who had the least amount of exposure seem to be at greater risk for allergies and asthma.
This is the first study in which the potential beneficial effects of the hygiene hypothesis are not confined to farm children. Hopefully further research by his group and others will help give us a better understanding of those factors that may be protective against the development of allergy and asthma.
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