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Correction Appended: March 5, 2010

In 2008, Gideon Lack of King's College London published a startling study comparing the rate of peanut allergies in children in London with that of children in Tel Aviv. The study of 10,000 Jewish children, which appeared in the Journal of Allergy and Clinical Immunology, found that kids in the U.K. were almost 10 times as likely to have a peanut allergy as their peers in Israel, says Lack.

Why the disparity? Although Lack can't draw conclusive explanations from his observational study, he suggests that one reason may have to do with early exposure. In Israel, children are typically introduced to peanuts much earlier than in Europe and North America. Lack points to a popular Israeli snack food called Bamba (like peanut-flavored Cheez Doodles), which youngsters start eating as early as infancy. That early exposure may desensitize children to peanuts, even in kids with a family history of food allergies.

The theory has gained enough traction that the National Institutes of Health is funding a seven-year study, also led by Lack, involving 640 children at high risk of allergy. Half of the study participants will avoid peanuts, while the other half will consume them regularly from 11 months to 3 years of age. Researchers will measure the rate of allergy in both groups by age 5.

The findings, which are expected by 2014, could mark a significant change in the way doctors handle food allergies. The conventional treatment has long been no treatment at all — essentially, patients are simply advised to avoid problem foods altogether. But a growing number of studies indicate that such an approach may someday be a thing of the past.

In a recent experiment presented at the February meeting of the American Association for the Advancement of Science, Andrew Clark of Cambridge University recruited 23 peanut-allergic children and fed them precise doses of crushed peanuts every day. At first they showed the typical allergic reactions: lots of itching, coughing and reddening of the skin. But after just three months, most of the kids were able to eat five peanuts a day with no reaction; at the end of year, the majority of them could safely eat 32 peanuts, which meant they no longer needed to read food labels for possible nut contamination. Clark has just embarked on a three-year, $1.5 million controlled trial to test the same treatment in 104 children with peanut allergies. Similar studies are also under way at Duke University and Mount Sinai Medical Center in New York City, among other places.

The experimental treatment, called oral immunotherapy, aims to desensitize the body to allergens like peanuts by training the immune system to make peace with them. Most food allergies — whether to peanuts, eggs, milk or shellfish — are a result of the immune system misidentifying a food as a dangerous toxin. The body wages war with the invader, and the by-product is an allergic reaction — anything from a minor itch or swelling to a severe asthma attack, which in extremely rare cases and if left untreated can lead to death. Immunotherapy is designed to build up the body's tolerance to such "toxins" by gradually increasing patients' exposure to them over several weeks or months, says Hugh Sampson, who runs the Jaffe Food Allergy Institute at Mount Sinai. "We start at the microgram level, scale up to milligrams and may end with grams [of peanuts]," says Sampson, but he warns people not to try the program at home. "Every patient has an adverse reaction when we increase the dose," and in severe cases, the patient may need immediate medical attention.

The evidence so far seems to suggest that many cases of milk, egg, peanut and wheat allergies can be treated, at least in the short term. In human studies, tolerance to problem foods appears to last as long as the treatment is in progress. "The question is, Is this just a treatment, or can it be a cure?" asks Cambridge University's Clark, whose study on toddlers is designed to help furnish an answer.

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.

• Adi Narayan
• The conventional treatment for allergies to foods like peanuts, eggs, milk or shellfish has been no treatment. But recent studies suggest a new approach