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KAI RYSSDAL: There are about 12 million people in this country who have food allergies. If one or more of them live in your house, then you're probably familiar with the art of deciphering labels. Trying to figure out which product may or may not contain something that's going to set off a reaction. But the different ways manufacturers list ingredients makes figuring out whether something's safe to eat tricky at best.

Tomorrow the Food and Drug Administration's going to look into those voluntary labels and whether confusion is damaging confidence.

From the Marketplace Sustainability Desk, Sarah Gardner reports.

SARAH GARDNER: You know the labels. The ones that say things like "may contain traces of peanuts." The food isn't supposed to contain peanuts but a small amount may have accidentally contaminated the food during manufacturing. I found a bunch of those warnings in my own cupboards.

GARDNER IN KITCHEN: Says manufactured in a facility that uses wheat, milk, eggs, soy and tree nuts. So what does that mean?"

ANN MUNOZ-FURLONG: Right now it's like the Wild West. Nobody knows what's going on.

Anne Munoz-Furlong is founder of the Food Allergy and Anaphylaxis Network. Furlong says right now the FDA doesn't regulate these kinds of labels and the language varies widely. She's seen everything from "may contain the occasional nut" to "processed in a nutty facility." No pun intended.

Furlong says the vague language may protect companies from liability, but it's confusing consumers.

FURLONG: What's the difference between "may contain peanuts" and "processed in a facility?" Is the risk the same? We have no idea.

Plenty of food allergy watchers are skeptical about these warnings.

"Is it me, or are allergy labels getting way wackier?" asked a mother of two on the "Nut-Free Mom Blog." She cites a label on a sugar product warning of possible contamination from eight food allergens, including shellfish.

Recent surveys show some allergic consumers are beginning to ignore the warnings.

Kim Lutz has a young son allergic to eggs, dairy and walnuts. She says she pays attention to them.

KIM LUTZ: On the flip side, I've talked to other families who say, "Oh, they're just trying to cover themselves from litigation." And I'm sure it's perfectly fine, because it's so vague and they are feeding their kids those things.

That's a dangerous gamble, according to researchers, especially since some allergic reactions can be fatal. University of Nebraska food scientist Steve Taylor tested over 100 products with two differently worded peanut warnings. He found more of that allergen in the products labeled with the milder-sounding warning.

STEVE TAYLOR: It's important for consumers to understand, allergic consumers, that all of these statements are intended to serve the same purpose: Please do not eat our products.

Taylor, though, suspects some companies slap on a warning rather than spend money on good risk analysis. Tomorrow, activists will push the FDA to set some standards for these labels. Industry officials are expected to resist new mandates but appear open to discussion. Some say they'd welcome more guidance.

Alison Bodor at the National Confectioners Association says candy makers want more data on what levels of allergen would trigger the need for labeling.

Alison Bodor: Right now we're operating more or less on a zero-tolerance basis, meaning that any amount of allergen in that product is too much. And in that situation the manufacturer's always going to err on the side of protecting the consumer.

Scientist Steve Taylor says his research should soon yield some useful risk data, at least for peanut allergies.

Activists like Furlong hope tomorrow's hearing will lead to, at least, more standardized language and an end to some of the more absurd labels. Furlong recently spied a jar of peanuts with a warning label reading "may contain peanuts."

I'm Sarah Gardner for Marketplace.

Statement from the Grocery Manufacturers Association on the FDA hearing:

"Our members are committed to ensuring that food-allergic consumers have the information they need on the food label to make informed choices about whether or not a particular food item is appropriate for them to eat. That is why we support the use of science-based criteria by food and beverage companies in determining whether or not a supplemental or 'may contain' allergen advisory on a food product label is necessary."