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According to a new study, exposing toddlers to a combination of certain allergens and bacteria can help reduce the children's risk of developing wheezing and allergic diseases. The researchers reported that exposure should ideally occur before the toddlers turn one.

In this study, which was funded by the National Institutes of Health (NIH), the researchers examined data gathered by the Urban Environment and Childhood Asthma (URECA). URECA has enrolled 560 children since it started in 2005. The children were from four large cities, which were Baltimore, Boston, New York and St. Louis. They were all considered high risk for asthma or allergies because they had at least one parent with these conditions.

The researchers tracked the infants and measured their frequency of wheezing episodes. They also recorded the levels of the five most common allergens that exist in the inner-city, which were cat, cockroach, dog, dust mite and mouse. The team found that exposure to cockroach, mouse and cat within the first year of life was tied to a reduced risk of wheezing by the time the infants turned three.

In a smaller study that also examined data from the URECA sample, researchers divided 104 children into four groups, which were wheezing only, allergen-sensitivity only, wheezing and allergen-sensitivity, and neither. They discovered that children who did not have wheezing or sensitivity at the age of three were more likely to have been exposed when they were one. The combination of bacteria mainly included those found in house dust. The researchers identified the bacteria as belonging to the Bacteriodes and Firmicutes.

"These observations support the emerging concept that early-life exposure to high bacterial diversity may protect kids from developing allergies. Most importantly, the findings show that this protection is even stronger when children also encounter high allergen levels during this time," written in the press release.

The study, "Effects of early life exposure to allergens and bacteria on recurrent wheeze and atopy in urban children," was published in the Journal of Allergy and Clinical Immunology.