"This suggests that (allergies) might be genetic," Kim said, something scientists have long suspected.
But it's not like a genetic disease that's 100 percent inherited. "There's no one gene for allergies or asthma. It's probably a combination of multiple genes interacting somehow with the environment."
Up to 50 million Americans have some kind of allergy, according to the American College of Allergy, Asthma & Immunology.
Jonathan Silverberg, a dermatologist at St. Luke's-Roosevelt Hospital Center in New York, recently analyzed data from more than 91,000 children to determine whether children born outside the United States were as likely as American children to develop allergies.
He found that foreign-born children residing in the United States had half the risk of developing allergies than those who were born here. That was true for all types of allergies, including food allergies, although the association was strongest for asthma.
Silverberg and his colleagues started the study after realizing they were seeing foreign-born children at their practice developing allergies much later in life. They found that the foreign-born kids who lived in the United States for more than 10 years had a higher prevalence of allergies than the children who had only been in the country for a couple of years.
Scientists know that environmental exposures play a role in allergic disease; you can't be sensitized to something you've never been exposed to. But in the past researchers have focused on allergens in the air, Silverberg said, such as pollen or ragweed, instead of other environmental exposures. These other factors could be related to a child's climate, diet or geography-specific infections.
"What (this study shows) is that there's something about what we're experiencing in the U.S. compared to many other countries that seems to really lead people to, or unmask, allergic disease," he said.
Which factor -- if any -- plays the dominant role is so far unclear.
It's hard to make any practical conclusions from these kinds of studies, Silverberg said. But eventually knowing where allergies come from could help us figure out a way to prevent them, or at least treat them more effectively.
Then allergy sufferers will be able to frolic in the flowers and roll in the grass and eat peanuts just like everyone else.