A seemingly harmless snack leads to hives and itching and swelling of the throat, even trouble breathing—a terrifying experience that threatens a growing number of kids (and their moms and dads). For reasons not totally understood, food allergies—to peanuts and eggs and fish, for example—are on the rise, and affected children are two to four times as likely as unaffected kids to have related conditions such as asthma or other allergies. About 3 million children under 18 had food allergies in 2007, says the Centers for Disease Control and Prevention—18 percent more than in 1997. All told, about 6.8 million children suffered from some sort of allergy in 2006.
Why the increase? Improved diagnosis is one likely cause, but allergies do also appear to be more common today than a generation ago, says Andy Liu, associate professor of pediatrics at National Jewish Health, the Denver medical center that specializes in lung, allergy, and immune diseases. One factor that may be driving an increase in both food and environmental allergies: a shift away from farm living and toward scrupulous cleanliness. The "hygiene hypothesis" holds that the immune system benefits from early exposure to bacteria. "The more hygienic your environment, the more allergic you will be," says Leonard Bielory, director of the division of allergy, immunology, and rheumatology at the New Jersey Medical School. Similarly, it's possible that a lack of exposure to specific foods in infancy may result in allergies to those foods later.
Managing symptoms. Once an allergy sets in, you're stuck managing symptoms. So, many new parents wonder: Is it possible to prevent allergies from developing in the first place? To date, "we don't have a good handle" on how to prevent allergies, says Liu; research on that front has been limited, and the causes of allergies are a complex mixture of genetics and environment. One long-awaited study of 8,600 Jewish children in the United Kingdom and Israel, published in November in The Journal of Allergy and Clinical Immunology, hints that with food allergies, at least, there might be a benefit from early exposure. The researchers found that kids who were not exposed to peanuts during infancy or early childhood were 10 times as likely to end up with a peanut allergy as those who ate peanuts.
The study depended on retrospective information about eating habits, but a clinical trial by researchers in the United Kingdom is currently recruiting 480 children ages 4 months to 10 months who will be randomly assigned to consume or avoid peanuts. Results are expected in about five years. There is also some hope that oral immunotherapy, which involves gradually increasing an allergic person's exposure to offending foods, might help ward off allergies in nonallergic people, says Wesley Burks, an allergist and professor of pediatrics at Duke University Medical Center who has studied immunotherapy. But that remains to be proved.
For now, the American Academy of Allergy, Asthma and Immunology recommends adding vegetables, rice, meat, and fruit to a child's diet between 6 months and 1 year of age—one by one, so that problem foods can be easily identified. After the child is 1, it's OK to try milk, wheat, corn, citrus fruit, and soy. At age 2, eggs are allowed and, at 3, fish and peanuts. Last July, the American Academy of Pediatrics Committee on Nutrition published guidance on protecting children considered to be at high risk. (If one parent has allergies, a child has a 48 percent risk of developing allergies; if both parents are allergic, the risk increases to 70 percent, according to the AAAAI.) "Generally effective" protective strategies include breastfeeding for the baby's first four to six months of life (or sticking with low-allergenic infant formulas) and holding off on solid foods until the baby is 4 to 6 months old. Strategies that "remain unproven," according to the report, include limiting mom's diet during pregnancy or breastfeeding. Perhaps reflecting the value of early exposure, some research has shown that that strategy may actually raise the odds of later trouble.