WASHINGTON – It is one of the biggest frustrations of life with food allergies: That hodgepodge of warnings that a food might accidentally contain the wrong ingredient.

The warnings are voluntary – meaning there is no way to know if foods that do not bear them really should. And they’re vague: Is “may contain traces of peanuts” more reliable than “made in the same factory as peanuts?”

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 whose son Tommie, almost 8, is allergic to peanuts, dairy, wheat and five other ingredients.

But she does not 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.

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.

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.”

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.