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Too-Clean Homes May Encourage Child Allergies

Exposure to a little dust, dander in infancy might prime tots' immune systems, research finds


They found that infants who grew up in homes with mouse and cat dander and cockroach droppings in the first year of life had lower rates of wheezing at age 3, compared with children not exposed to the allergens.

Wheezing was three times as common among children who grew up without exposure to such allergens, affecting 51 percent of children in "clean" homes compared with 17 percent of children who spent their first year of life in houses where all three allergens were present.

Household bacteria also played a role, and infants in homes with a greater variety of bacteria were less likely to develop allergies and wheezing by age 3.

Children free of wheezing and allergies at age 3 had grown up with the highest levels of household allergens and were the most likely to live in houses with the richest array of bacterial species, researchers found.

"The combination of both -- having the allergen exposure and the bacterial exposure -- appeared to be the most protective," Wood said.

Both Wood and Mahr cautioned that these findings need to be verified, and that parents shouldn't make any household decisions based on them.

For example, parents shouldn't adopt a dog or cat assuming that its presence will help immunize their kids against allergies and asthma, Wood said. At the same time, they shouldn't ditch their family pet, either.

"We would not take any of this as information we could use to give advice," Wood said. "Please don't get an intentional cockroach infestation in your house. There's no reason to think that would help."

There are a number of other factors that could influence the likelihood that an inner-city kid will develop asthma, including tobacco smoke, high levels of household stress, or even exposure to the same sort of potentially beneficial allergens too late in life, past their first birthday, Wood said.

"This is by no means a simple story," he said. "There could be a lot of factors going on."

Mahr said the findings could someday lead to treatments that would help infants build up resistance to allergies. "I can see someone coming up with a spray. You'd spray the crib that the kid sleeps in every so often, and let the kid crawl around in it," he said.


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