When you are shopping for someone who has a food allergy, a trip to the grocery store is like a police investigation. Each product must be scrutinized. Labels are examined, each ingredient studied.

My 5-year-old son, Alexander, is allergic to almonds and hazelnuts, so my wife and I spend a lot of time trying to decipher food labels. If you miss something, even one word, you risk an allergic reaction.

Although federal law requires manufacturers to include allergen warnings on prepackaged foods, it is not always clear which products contain allergens and which do not. The regulation does not cover all types of foods, nor instances in which trace amounts of allergens may be present.

This has created a confusing and risky marketplace for my family and millions of others — roughly 8 percent of children have a food allergy.

I set out to better understand allergen labeling and the problems consumers face. Here’s what I learned:

WARNINGS FOR CERTAIN ALLERGENS

Congress passed the Food Allergen Labeling and Consumer Protection Act in 2004, a rule book for manufacturers. Companies must place special warnings on prepackaged foods if they were made using certain allergens: milk, eggs, fish, shellfish, peanuts, wheat, soybeans and tree nuts.

If I grab a box of cookies from the store shelf, I might find a special warning printed near the ingredients list — “contains almonds” — because almonds are part of the tree nut family. If I don’t see one, I can be assured that the product wasn’t made using almonds.

SOME ALLERGENS AREN’T ON LABELS

Sesame is the ninth-most-prevalent food allergy among adults in the United States. But the food was left off the list of major food allergens in the labeling law passed by Congress.

Manufacturers do not have to print a “contains sesame” message. It may even be hidden under “natural flavors” or “spices” on the ingredients label.

The Food and Drug Administration is considering whether to add sesame to the list of major allergens as is already mandated in Canada, the European Union and Australia.

TRACE AMOUNTS DIFFICULT TO TRACK

Here is where it gets even more complicated. Even if my box of cookies does not include one of the mandated warning labels, the cookies may still contain an allergen.

Let’s say, back at the manufacturer, my cookies were put on the same conveyor belt used for almond cookies. Small bits of almond might have made it into my seemingly almond-free cookies.

This is called cross contact. And there is no surefire way I can know it happened — the federal government does not require manufacturers to include labeling for possible cross contact of allergens.

As a result, food manufacturers developed their own unregulated labeling practices to alert consumers to potential cross contact. Here’s a sampling from a recent trip to the grocery store:

>> Cookies: “May contain peanuts and tree nuts.”

>> Chocolate bar: “Manufactured on the same equipment that processes almonds.”

>> Bread: “Made in a bakery that may also use tree nuts.”

These short descriptions, often called “precautionary allergen labeling,” may alert consumers to some risks, but because the labels are unregulated, their meanings differ from company to company.

“The whole world of food labeling is almost like a foreign language,” said Allison A. Ososkie of Vienna, Va., whose 2-year-old son is allergic to egg, milk, peanuts, tree nuts, soy and shellfish.

A 2017 study, published in The Journal of Allergy and Clinical Immunology: In Practice showed consumers made “risk assessments” based on the words used in this kind of labeling.

“We’re making consumers decide, based on the wording of that precautionary allergen label, what seems safe for themselves or their child, and I think that’s a huge issue,” said Dr. Ruchi S. Gupta, a professor of pediatrics at Northwestern Medicine in Chicago and an author of the study.

SOMETIMES LABELS ARE JUST WRONG

Another issue is incorrect packaging. Sometimes, during the manufacturing process, food made using one of the eight major allergens is not properly labeled.

In 2018, about one-third of FDA recalls involved prepackaged foods that were erroneously labeled, according to data compiled by the agency.

IT DOESN’T GET BETTER AT BAKERY, DELI

Let’s say I head over to the store’s bakery for freshly prepared treats. Sadly, foods produced in a bakery or deli and “placed in a wrapper or container in response to a consumer’s order” are not covered under federal labeling requirements. Packaged by a bakery worker, my purchase will not have any federally regulated allergen labels on it.

MANUFACTURERS SAY SAFETY IS PRIORITY

The labeling on the side of my box of cookies — whether it says “contains almonds,” “may contain almonds” or nothing at all — is determined by the food manufacturer.

So what goes into making the food that ends up on a shelf? And what kind of consideration is given to people with food allergies?

At Nestle’s U.S. operation, the key is applying “allergen management” across the expansive and complex operation, said David C. Clifford, director of food safety at Nestle USA. He described the company’s approach as “objective, science-based, risk-based” with allergen training throughout the company.

FOOD FOR THOUGHT

Recommendations for finding safe food:

>> Skip food with precautionary labels: When you’re scanning the shelves, if you spot precautionary labels beginning with “may contain” or “processed in the same facility as,” don’t buy the products if the labels refer to your allergy, said Dr. Scott H. Sicherer, chief of pediatric allergy and immunology at the Icahn School of Medicine at Mount Sinai in New York.

“You shouldn’t make risk decisions based on what precautionary words are used on the label,” Sicherer said. “But rather, to be 100 perfect safe, just avoid products that have the precautionary label, if that’s a food that you’re avoiding.”

>> Reach out to food manufacturers: Instead of guessing what a label might mean, a few parents I spoke to take a proactive approach: calling companies to get answers, even if it is time-consuming.

“Maybe once a month I’m calling and trying to track something down,” said Julie V. Lunn, a bookkeeper and entrepreneur in Havre de Grace, Md., whose 3-year-old daughter is allergic to a variety of foods.

>> Find products from allergen-free sites: One way to simplify things is to seek out products made in allergen-free plants.

Enjoy Life Foods has one such plant, said Joel D. Warady, general manager of the company. He said employees were forbidden from bringing peanuts to work, and they must wear company-issued shoes that don’t leave the factory, in Jefferson, Ind.

MadeGood Foods, based in Vaughan, Ontario, swabs hands and tables to test for allergens, said Janice A. Harada, the company’s marketing manager.

Manufacturers like these cater to the allergy community, using branding to make it clear their foods are free of allergens.

And that box of cookies I’ve been looking for? If its label says “made in a dedicated allergen-free facility,” it should be safe to give to my son.

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