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Children born outside the United States have lower rates of allergies, but after prolonged U.S. residence, reduced prevalence is reversed, researchers say.

Dr. Jonathan I. Silverberg of St. Luke's-Roosevelt Hospital Center and colleagues at the State University of New York Downstate Medical Center and Oregon Health Science Center examined a sample of nearly 92,000 children from the 2007-08 National Survey of Children's Health.

They investigated if there was an association between birthplace, length of U.S. residence and rates of asthma, eczema, hay fever and food allergy.

After statistical analysis of the sample, the researchers found compared with the U.S.-born children, the children born outside the United States indeed had lower rates of allergic disease.

Silverberg and colleagues also discovered children who had parents who were also not U.S.-born had lower rates for all of the allergic diseases versus those children whose parents were born in the United States.

"Most interestingly, our research with this sample uncovered children whose birthplace was outside the United States who then lived here for more than 10 years had higher odds of developing eczema and hay fever when compared with those who had lived here for up to two years," Silverberg said. "However, we did not find this was true for asthma or food allergy."

What we can take away here is that seeing this loss of childhood protection from eczema and hay fever after extended U.S. residence implied environmental factors may promote the development of allergic disease," Silverberg explained.

The findings were presented at the annual meeting of the American Academy of Allergy, Asthma & Immunology.