Children born outside the United States have a lower risk of asthma, skin and food allergies, and living in the United States for a decade or more may raise the risk of some allergies, said a study Monday.
The research in the Journal of the American Medical Association suggests that certain environmental exposures could trigger allergies later in life, overcoming the protective effects of microbial exposure in childhood.
The study examined records from 2007-2008 phone surveys of nearly 92,000 people in the United States, where food and skin allergies have been on the rise in recent years.
Allergies reported in the survey included asthma, eczema, hay fever, and food allergies.
“Children born outside the United States had significantly lower prevalence of any allergic diseases (20.3 percent) than those born in the United States (34.5 percent),” said the study led by Jonathan Silverberg of St. Luke’s-Roosevelt Hospital Center in New York.
“However, foreign-born Americans develop increased risk for allergic disease with prolonged residence in the United States,” it said.
Children who were born outside the United States but came to live in the United States for longer than 10 years showed “significantly” higher odds of developing eczema or hay fever but not asthma or food allergies, said the research.
“These data indicate that duration of residence in the United States is a previously unrecognized factor in the epidemiology of atopic disease,” it said.
“Further, this suggests that foreign-born US residents might be at increased risk for later onset of allergic disease.”
Previous research has shown that children who grow up in developing nations tend to have lower rates of allergies, and experts believe this is because they are exposed to more infections and microbes that build up their immune systems.
Allergies are essentially a symptom of a hypersensitive immune system, reacting to substances that should normally be considered harmless.
The JAMA study noted that the United States may not be alone in this phenomenon, since previous studies have found that immigrants in Italy, Israel, and Australia had lower allergy rates than natives.
More research is needed to find out if allergies increase in those countries among immigrants who live there for long periods, said the study.