Now health officials in the U.S. and Canada are debating setting standards, amid increasing concern that consumers are so confused they're starting to ignore the warnings.
"Really, the safest thing you can do is make all your food at home from scratch, period," says Margaret Sova McCabe of Sanbornton, N.H., whose son Tommie, almost 8, is allergic to peanuts, dairy, wheat and five other ingredients.
But she doesn't find that practical -- and repeatedly has spotted longtime favorite "safe" foods suddenly bearing new warnings that accidental contamination is possible after all.
"Sometimes we buy the product anyway, and sometimes we don't," says McCabe, who is a law professor and questions how often the warnings signal liability protection rather than true risk.
"What does this really mean? Can I count on it, as a consumer, to really have any meaning?" she asks.
The Food and Drug Administration will ask those same questions at a public hearing on Sept. 16, a first step toward developing what it calls "a long-term strategy" to clear the confusion.
"Advisory labeling may not be protecting the health of allergic consumers," the FDA acknowledged.
Canadian authorities have gone a step further, saying accidental-allergy warnings are "misleading consumers" and advising food makers to begin clarifying them even as Health Canada researches a formal policy.
The food industry recognizes there's confusion. The Grocery Manufacturers of America has been working to set new guidelines on the warnings for more than a year, but declined comment before next month's meeting.
About 12 million Americans have food allergies. Severe ones trigger 30,000 annual emergency-room visits, and 150 to 200 deaths a year.
Starting in 2006, a U.S. law required that foods disclose in plain language when they intentionally contain highly allergenic ingredients such as peanuts or dairy.
Left out of the law are accidental-allergy warnings -- for foods that might become contaminated because they were made in the same factory, or on the same machines, as allergen-containing products. The FDA has said that a quarter of inspected food factories have the potential for such a mix-up.
More and more foods bear precautionary labels, but there's a disconnect. The Food Allergy & Anaphylaxis Network, an influential consumer group, counts at least 30 different ways that the warnings are worded -- and consumers too often falsely assume that one food is riskier than another because its label sounds scarier.
Three-quarters of parents of food-allergic children surveyed by the group in 2006 said they would never buy a food with an accidental-allergy warning, down from 85 percent in 2003, when such labels were novel.
The FDA's own surveys found the allergic pay more attention to warnings that a food "may contain" an allergen than those "made in the same factory" labels.
Yet when University of Nebraska researchers tested nearly 200 products with various accidental-peanut warnings, they found that peanuts were more likely to have sneaked into products labeled "made in the same facility."
And Health Canada researchers recently discovered that some chocolate labeled as possibly containing "traces" of peanuts or tree nuts in fact contained up to six times the amount that the government considers a trace level.
Contributing to consumer mistrust are puzzling warnings, like canned or frozen vegetables with nut precautions. Just last week, allergy network founder Anne Munoz-Furlong was stunned to receive a basket of fresh fruit with a warning that it might contain nuts or milk.
"Right now everybody's making up their own rules," Munoz-Furlong says -- and she's pushing FDA for clear standards to help consumers understand which foods to avoid.
In Canada, the government's review is just beginning, but meanwhile it recommends foods bear one of two labels: "May contain X allergen" or "Not suitable for consumption by persons with an allergy to X."
Back in New Hampshire, the McCabes show how tricky label reading is. Tommie has loved a particular nondairy soy yogurt since infancy. When it began bearing an accidental-allergy precaution, his mother toured the factory and was relieved by how the equipment was cleaned. But last week, she noticed the label had changed again, to say the yogurt might also contain live cultures based on milk.
It "maybe illustrates how difficult it can be when you have food allergies to stay on top of that information," McCabe said.
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