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Infant exposure to allergens may help prevent wheezing

Exposure to certain allergens and bacteria within the first year of life may protect children from wheezing and allergies. The study's findings suggest potential strategies for preventing asthma.

Asthma is a chronic (long-term) illness that affects the lungs. The airways become inflamed and narrow, causing difficult breathing, wheezing (a whistling sound while breathing), tightness in the chest, and coughing.

Risk factors for developing asthma include recurrent wheezing in early childhood and sensitivity to some types of common allergens, such as cockroach and mouse. On the other hand, studies suggest that exposure to certain microbes early in life may protect against allergies and asthma.

The Urban Environment and Childhood Asthma study aims to identify factors that contribute to asthma development in children from inner city settings, where allergies and asthma are more common and severe. Since 2005, researchers have enrolled 560 children from 4 cities: Baltimore, Boston, New York, and St. Louis. The children have at least one parent with asthma or allergies, placing them at high risk for developing asthma. They are being followed from before birth until age 16. The study is funded by NIH's National Institute of Allergy and Infectious Diseases (NIAID) and National Center for Advancing Translational Sciences (NCATS).

The children were tested for reactions to various allergens at periodic clinic visits. Wheezing episodes were reported by parents. Homes were visited annually to collect household dust samples from the living room and child's bedroom. The dust was tested for 5 common inner city allergens: cat, cockroach, dog, dust mite, and mouse. In a subset of 104 children, the bacterial content of house dust collected in their first year of life was also assessed.

An evaluation of the children through age 3 appeared online on June 6, 2014, in the Journal of Allergy and Clinical Immunology. As expected, cumulative allergen exposure over the first 3 years of life was associated with allergies and wheezing at age 3, and children with allergy were more likely to have recurrent wheezing. Surprisingly, however, children with the highest level of exposure to allergens from cockroaches, mice, and cats during their first year were least likely to have recurrent wheezing at age 3.

Children who were exposed during their first year of life to a greater variety of bacteria-particularly from the phyla Bacteriodetes and Firmicutes-were also less likely to wheeze at age 3.

"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," says principal investigator Dr. Robert Wood of Johns Hopkins University School of Medicine.

"If other studies confirm these findings, it might suggest that permitting allergen exposures, with increased exposure to certain microbes or to their sources, might be more successful in reducing asthma risk," says Dr. Homer Boushey of the University of California, San Francisco, another principal investigator.

--From the National Institute of Health

For further information on this and other health topics, visit the web site of the National Institute of Health at

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