Infants exposed to a diverse range of bacterial species in house dust during the first year of life are less likely to develop asthma in early childhood, says a new study.
Children who were neither allergic nor prone to wheezing as three-year-olds were the most likely to have been exposed to high levels of bacteria, and paradoxically, to high levels of common allergens.
"There is no obvious mechanism explaining the association, but the evidence supports earlier research that strongly pointed to the influence of microbial species in shaping immune responses," asserted Susan Lynch, an associate professor of medicine at the University of California, San Francisco (UCSF).
Lynch and UCSF pulmonologist Homer Boushey compared exposure to allergens from cat, cockroach, dog, dust mite and mouse, and wheezing incidence as told by parents and allergy as assessed by tests.
Through the first three years of life, cumulative exposure to allergy-provoking substances from cats, mice, cockroaches and dust mites - but not from dogs - was associated with more wheezing and allergic reaction in the new study.
These results indicate that immune responses might be shaped by exposure during the first year of life differently than they are by later exposures.
"The concomitant exposure to high levels of certain allergens and bacteria in early life may be beneficial," the researchers concluded.
The report was published in Journal of Allergy and Clinical Immunology.
