There are two completely different kinds of allergen information on a package, printed in the same typeface, inches apart. One is required by federal law. The other is a sentence the manufacturer chose to write, in wording nobody checks, for reasons they never have to explain.
Knowing which is which does not make the decision easier. It does make it an informed one.
What the law actually requires
The Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA) requires packaged foods regulated by the FDA to declare the major food allergens they contain as ingredients. There are nine of them: milk, egg, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans, and — since the FASTER Act took effect on January 1, 2023 — sesame.
The declaration has to name the food source in plain language, either in the ingredient list itself or in a separate “Contains” statement after it. That is why a label can say whey (milk) rather than leaving you to know that whey is a milk protein, and why a bar with sodium caseinate in it must have the word milk somewhere on the package.
This part is enforceable. If a product contains a major allergen as an ingredient and does not say so, that is a labeling violation and a recallable one.
What "may contain" is instead
Everything else — may contain traces of peanuts, manufactured on shared equipment with tree nuts, processed in a facility that also processes milk — is called advisory or precautionary allergen labeling, and it is a different thing entirely.
It is voluntary. It is not standardized. Specifically:
- No law requires it. A manufacturer whose line runs peanut products before yours is under no federal obligation to tell you.
- The wording means nothing in particular. “May contain” and “made in a facility with” are not defined terms and are not ranked by risk. Two companies can use opposite phrasings to describe identical production lines.
- There is no threshold behind it. The statement does not tell you whether the possible amount is a detectable trace or something more. As of 2026 the FDA has begun publicly consulting on whether to move precautionary labeling to a threshold-based system — which is an acknowledgement that today it carries no quantity information at all.
The part that catches parents out
Because the statement is voluntary, its absence is not information.
A package with no advisory warning has not been certified free of cross-contact. It may have been made on a dedicated line — or it may have been made on a shared one by a company that simply does not use advisory labels. You cannot tell the two apart from the outside of the box.
The practical rule most allergists give
If an advisory statement names your child’s allergen, treat the product as unsafe. If there is no statement at all, that is not the same as a guarantee — and for a child with a history of anaphylaxis, calling the manufacturer is the only way to actually find out how the product is made.
This is also why “we’ve bought it before” is not a safe check. Formulations and production lines change without any change to the front of the package, which is the single most common way a familiar product becomes a problem.
Where "free from" claims are different
One useful contrast: gluten-free is a regulated claim. The FDA defines it, and a food bearing it must contain less than 20 parts per million of gluten. That is a number a manufacturer can be held to.
There is no equivalent federal definition for “peanut-free” or “dairy-free” on a package. Those are marketing phrases. Third-party certifications exist and some are rigorous, but they are the certifier’s standard, not a legal one — and worth reading up on individually rather than treating the seal as a category.
“Non-dairy” is the sharpest example: it is a dairy-industry term of art, and non-dairy products routinely contain caseinate, which is a milk protein. A milk-allergic child can react to a product whose front label says non-dairy. The ingredient list will still say milk, because FALCPA requires it — which is exactly why the ingredient list, not the front of the box, is the thing to read.
What to do with a package, in order
- Read the ingredient list and the Contains statement. This is the legally binding part. If your allergen appears here, stop.
- Read the advisory statement, if there is one. If it names your allergen, treat it as a no.
- Notice if there is no advisory statement. Absence is not clearance — decide with your allergist how your family handles unlabeled cross-contact risk.
- Re-read every time. Including on the product you buy every week.
Step four is the one that gets skipped, and it is the one automation genuinely helps with — not because a scanner knows more than you do, but because it does not get tired on the fourth aisle with a toddler in the cart.