For scientists studying food allergies, peanuts have become a particularly elusive adversary.
There’s still no consensus on why the incidence of peanut allergies quadrupled in the United States in just over a decade. To complicate matters further, the advice on when babies should first try peanut-containing products has changed dramatically in that time.
Fifteen years ago, doctors told parents to wait until their babies were 3 years old before giving them peanut butter, eggs, and fish—the idea being that young immune systems couldn’t yet handle such foods. By 2008, the American Academy of Pediatrics had retracted those guidelines, suspecting that “we might have caused this increase [in allergies] by telling people not to eat these things," the pediatrician and food-allergy researcher Scott Sicherer told me last year.
Then came a landmark study: Last year, the New England Journal of Medicine published the results of long-awaited research finding that the introduction of peanuts to children in infancy “significantly decreased” a child’s likelihood of developing a peanut allergy. Kids who first tried peanuts as infants—in the first 11 months of life—ended up having an 81 percent lower rate of peanut allergy by the time they were 5 years old, compared with kids who avoided peanuts in that time.