A latest study claims that children and teenagers who immigrate to the U.S. are half as likely to get asthma and allergies as those born in the country, reports Reuters Health.
Parents of 80,000 children were surveyed between 2007 and 2008 for the study. It found that despite their race, income or previous country, they were susceptible to asthma and allergies in the U.S, although not as much the local residents.
The immigrant children had 39 percent chances of getting hay fever, 43 percent of getting eczema and 60 percent complained about some form of food allergy. Children whose one parent was born outside the U.S. reported lesser incidence of allergies.
"This is definitely something we see clinically and we're trying to better understand, what it is in our environment that's increasing the risk of allergic disease?" Dr Ruchi Gupta of the Northwestern University Feinberg School of Medicine in Chicago told Reuters Health. She did not participate in the research.
"Food allergies have increased tremendously," she told Reuters Health. "We do see people who come from other countries don't tend to have it, but immigrants who are maybe second generation, they're identical (to U.S.-born people)."
The researchers said they are not sure how does this happens.
But, Dr Gupta explains that according to her, this occurrence might be because of hygiene hypothesis. It is said that the U.S. children are too clean and their immune systems are usually not exposed to common allergens; or it might be the poor quality of American diets.
According to Dr Jonathan Silverberg of Beth Israel Medical Center and St. Luke's-Roosevelt Hospital Center in New York, other factors playing a vital role may be climate, obesity and various infections.
He told Reuters Health that the environmental factors in the U.S. cause respiratory allergies. "Children born outside the U.S. are likely not exposed to these factors early in life and are therefore less likely to develop allergic diseases."
"This suggests that the protective effects of the hygiene hypothesis may not be lifelong," the study authors wrote in the journal.
