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If childhood allergies could be prevented or cured or even weakened it could help quell many parents' outsize fear of them. "People disproportionately worry about getting extreme reactions or even dying after eating peanuts," says Clark. But while allergy experts agree that risks from food sensitivities are very real, the truth is that only a small fraction of patients develop life-threatening reactions.
In a study published in January in the Journal of Allergy and Clinical Immunology, British researchers found that among 79 children who tested positive for peanut allergy in blood tests, only nine exhibited allergic symptoms upon eating peanuts. That may be because blood tests, which detect Immunoglobin E (IgE), an antibody that hunts for foreign particles entering the body, are not always accurate. Some people with moderate amounts of IgE in the blood are classified as "food sensitive"; those with larger amounts of the antibody are most likely food allergic. But the blood test doesn't distinguish between the two conditions.
"We find that a fairly large population of patients are avoiding peanuts, but they don't really have an allergy," says pediatric-allergy expert David Rosenstreich of the Montefiore Medical Center in the Bronx, who was not involved in the study. Total avoidance may only exacerbate patients' sensitivity.
The only foolproof way to identify a food allergy is to do an oral food challenge, in which patients eat a variety of foods, some of which contain small amounts of the allergen. If the patient reacts, then he or she is definitely allergic. However, such tests are time consuming and can be done only in specialized medical facilities.
For now, when it comes to food allergies, many American parents as well as the government and the food industry prefer to play it safe. The Food Allergen Labeling and Consumer Protection Act, which went into effect in 2006, calls for a zero-tolerance policy, meaning that manufacturers must declare whether their products contain even the tiniest amounts of allergens. Given that modern food flavorings and additives contain so many components, it's unusual to find a food product that has no trace amounts of allergens, even if the main ingredients do not contain them. "Nearly 30% to 40% of food recalls are due to undeclared allergens," says Stefano Luccioli of the Office of Food Additive Safety at the Food and Drug Administration (FDA).
Fueling that trend is rapidly evolving technology that helps detect microscopic, seemingly insignificant amounts of allergen protein in foods. Whenever that happens, the FDA can order a recall.
Regulators in the European Union are trying to change the E.U.'s zero-tolerance policy. The region plans to adopt a common standard that would specify testing methods and establish thresholds for all food-related allergens. For instance, when it comes to gluten, the general consensus is that any concentration below 20 parts per million is too small to have a harmful effect, so new regulations would not require manufacturers to label foods that contain less than that cutoff.
The FDA, for its part, is sticking with its present standards. But discussions are in progress to determine whether thresholds can be established for each allergen, as the E.U. is doing, says Luccioli. "The [current policy] is that there is no such thing as a minimum threshold. If you can detect [allergens], then it's not a safe level," he says.
The original version of this article misstated that Britain's National Health Service is funding Gideon Lack's current study of peanut allergy in children. In fact, the study is being funded by the National Institutes of Health.