Researchers studying allergy rates suggest that foreign-born children who did not have allergies before they came to the United States were more likely to develop allergies after living here for a decade.

A team led by Dr. Jonathan Silverberg of St. Luke's-Roosevelt Hospital Center in New York City compared children born abroad who had lived in the U.S. for less than two years with children who lived in the U.S. for over ten years.

They found that the children who lived in the U.S. for over ten years were three times more likely to develop allergic disorders, especially eczema.

The findings were presented as an abstract during a poster session at the 2013 annual meeting of the American Academy of Allergy, Asthma, and Immunology (AAAI), and reported in MedPage Today.

According to the article, immigrant children start out at low risk for allergies, though their risk of developing them increases the longer they remain in the United States.

It is unclear why the length of residence in America could be correlated to allergy risk, and how the increased risk for immigrant children differs from the change in allergy risk as American-born children age.

Dr. Silverberg explains that allergic disorders are far less common in other countries like Mexico and China than they are in the United States, and speculates that this may be attributable to in part due to shifting factors including urban living, socioeconomic status, ethnicity, nutrition, weight gain, and pollutants.

Even after adjusting for ethnicity, socioeconomic status, and residence in an urban area, the researchers found that the length of American residence of foreign-born children was "a previously unrecognized factor in the epidemiology of atopic disease."

The study sample came from 78,853 participants in the 2007-2008 National Survey of Children's Health on the prevalence of allergic disorders. The sample included 1,989 children born outside of the U.S. and 76,864 U.S.-born children.

Parents answered questions about their children's previous diagnoses of allergic disorders like asthma, eczema, other skin allergies, hay fever, and food allergies. Researchers noted the place of birth of both the children and their parents, and how long the children had been living in the United States.

The researchers noted possible related factors like the families' household income, residence in an urban area, and how often they moved.

Research has long established a link between urban living and higher allergy rates - suggesting either that growing up in rural areas offers more protection against allergens, or that urban areas expose children to more pollutants that predispose them to allergies.

Among the 1,989 foreign-born children included in the study, the average age was 11.5 years old. Over half (53%) were Hispanic, 17% were white, and 12.5% were black. Almost all (95%) lived in an urban metropolitan area.

The results showed that the longer immigrant children lived in the United States, the more likely they were to develop allergies later in life.

Parents of the foreign-born children were far less likely to have an allergic disorder than the parents of American-born children in the sample.

"The odds of developing allergic disease significantly increased after residing in the U.S. for a decade or more," said Silverberg.

"This suggested that foreign-born U.S. residents might be at increased risk for later onset of allergic disease."

The findings, while striking, are still preliminary and have yet to be published. Since the presentation was based on a secondary survey, it is unclear how representative allergy rates in the survey sample of foreign-born children are of the general population of children born abroad.

Future studies assessing allergy risk among children in the United States who were born abroad should aim to be more representative of place of origin - 53% of immigrants to America are from Latin America and the Caribbean, 29% of whom are Mexican, and another 28% are Asian.

It is also still unclear what total percentage of the foreign-born children suffered from any allergies, and how that number compares to the percentage of native American-born children who suffer from allergies.

The AAAAI released statistics about allergy rates among American children in 2010, but did not distinguish between immigrant and native-born children.

Diagnoses of food allergies are on the rise in the United States, and the cause is still unclear.

According to 2010 United States Census Bureau data, the immigrant population is estimated to be almost 40 million people who were born abroad, or 13% of the overall population. Of those 40 million, 7% are under the age of 18.

If these researchers' findings are accurate, 2.8 million foreign-born children may be at a higher risk for developing allergies the longer they live in the United States.

These data and conclusions should be considered preliminary until published in a peer-reviewed journal. Via MedPage Today.