(RxWiki News) Americans are are no strangers to hay fever and other allergies. Yet Americans born outside of the US may have to deal with these conditions less than those born in the US.
A recent study found lower rates of allergies among US children born outside of US borders.
These children may have parents working in the military, multinational corporations, diplomatic corps or other jobs taking them out of the country.
Or their parents may have chosen to live outside of the US for other reasons.
"Ask your pediatrician about allergies."
The study, led by Jonathan I. Silverberg, MD, PhD, of the Department of Dermatology at Beth Israel Medical Center and St. Luke's–Roosevelt Hospital Center in New York City, looked at allergy rates among American kids born in the US and overseas.
The researchers used data from the 2007-2008 National Survey of Children's Health, which included responses related to 91,642 children, from newborn to age 17.
The researchers looked at the rates of asthma, eczema, hay fever and food allergies among the children and compared them to their place of birth.
The researchers found that children who were US citizens but born outside of the US were about half as likely to develop any of those conditions than children born in the US.
US children born outside the US were about half as likely (47 percent less likely) to ever develop asthma and were 66 percent less likely to have asthma at the time of the survey, compared to children born in the US.
The children born overseas were also 40 percent less likely to have food allergies, 57 percent less likely to have eczema and 61 percent less likely to have hay fever, compared to US-born children.
This reduced risk in the foreign-born children remained even after the researchers took into account the children's age, sex, race/ethnicity, household income, number of times the child had moved homes and the proximity of a child's home to metropolitan areas.
Among children born outside the US whose parents were also born outside the US, the risk of chronic skin disorders, such as rashes, was also lower than children whose parents were born in the US.
The lower risk of allergies appeared to remain with kids if they spent more time outside of the US.
The researchers compared the allergies among foreign-born, US-citizen children who lived in the US for longer than 10 years and foreign-born, US-citizen children who only lived in the US for less than two years.
The children who had been in the US for at least 10 years were five times more likely to have eczema than children who spent less than two years in the US.
The children spending more time in the US were six times more likely to have hay fever than the kids who spent less than two years in the US.
There was no difference in the risk of asthma or hay fever among the children who spent more times in the US, compared to those who lived less than two years in the US.
However, these conditions were associated with movement within the US.
"In the present study, asthma and hay fever were associated with history of moving to a new address, particularly in American-born children," the researchers wrote. "This may be caused by changes of both indoor and outdoor environmental exposures and/or psychosocial stress related to moving."
One possible reason for these results, the researchers suggested, is that children who are exposed to more germs earlier in life may develop immune systems that are less likely to develop autoimmune diseases.
Allergies are an autoimmune disease, which means the body's defense system is overreacting to small threats (allergens) that the immune systems of people without allergies would normally ignore.
"The findings of the present study are consistent with the broader hygiene hypothesis, which suggests that either infections or certain microbial exposures in early childhood may confer protection against atopic disorders," the researchers wrote.
"The odds of developing allergic disease dramatically increase after living in the United States for longer than 10 years," the researchers continued. "This suggests that the protective effects of the hygiene hypothesis may not be life-long and that subsequent exposure to allergens and other environmental factors may trigger atopic disease even later in life."
The researchers also pointed out that different family practices or types of moving might influence allergy risk.
"That is, parents born and raised outside the United States may, for example, follow a healthier diet or have foods with a different antigenic profile than typically encountered in the Western diet," the researchers wrote. "Some cultures more commonly use spices, such as curcumin, and green tea that have anti-allergy and inflammatory properties."
The study was published in JAMA Pediatrics on April 29. The research did not appear to use external funding. The authors declared no conflicts of interest.