The "May Contain" Warning: Should You Ignore It?

You’ve found the perfect snack. The ingredients look clean. No peanuts, no milk, no eggs. But then, you flip the package over and see it: a tiny sentence at the bottom that says, "May contain traces of peanuts."

Do you put it back? Or do you assume it’s just legal jargon to protect the company?

For millions of people with food allergies, this is a daily dilemma. This guide explains exactly what Precautionary Allergen Labeling (PAL) means, the legal reality behind it, the science of cross-contamination, and whether it’s ever safe to ignore.

The Short Answer

No, you should generally not ignore it. If you have an IgE-mediated food allergy (a risk of anaphylaxis), allergists and safety experts recommend avoiding products with "may contain" warnings. The risk of cross-contamination is real, and the amount of allergen present can be enough to trigger a severe reaction.

What Does "May Contain" Actually Mean?

"May contain" is a type of Precautionary Allergen Labeling (PAL). It is used by manufacturers to warn consumers that an allergen might be present in the food, not because it’s an ingredient, but because of cross-contact during production.

This isn't just about a stray peanut falling into the mixer. It's about microscopic proteins that can survive cleaning cycles.

The Legal Loophole

Here is the most confusing part for consumers: In the US (FDA), UK (FSA), and EU, precautionary labeling is largely voluntary.

• Mandatory: Manufacturers must list allergens that are intentional ingredients (e.g., "Contains: Wheat"). This is required by laws like FALCPA and the FASTER Act in the US.
• Voluntary: They are not legally required to use a "may contain" statement for cross-contamination risks.

This means two identical cookies could be made in the same factory on the same line. One brand might choose to print "May contain nuts" to be transparent, while the other brand might choose to print nothing at all. This inconsistency is why label reading is so difficult.

How Cross-Contamination Happens

To understand the risk, you need to understand how food is made. Factories are high-speed environments where multiple products are produced on the same equipment.

1. The "Push-Through" Method

Imagine a machine making milk chocolate. When it's time to switch to dark chocolate (dairy-free), they might not take the machine apart to clean it. Instead, they push the dark chocolate through until it looks black. The initial "transition" chocolate is discarded, but the final product might still contain traces of milk from the pipes.

2. The "Bakery Effect" (Airborne Dust)

In bakeries, flour dust hangs in the air. Even if a product is made on a separate table, wheat proteins can settle on it from the air. The same applies to peanut dust, which is sticky and hard to contain.

3. Cleaning Limitations

"Wet cleaning" (hosing down equipment) is effective, but many dry foods (like crackers or chocolate) require "dry cleaning" (scraping and vacuuming). Dry cleaning is far less effective at removing sticky allergen proteins.

The Science of Thresholds: How Much is Too Much?

How much peanut does it take to cause a reaction? Scientists use a metric called ED01 or ED05 (Eliciting Dose).

• ED01: The dose that triggers a reaction in the most sensitive 1% of the allergic population.
• ED05: The dose that triggers a reaction in 5% of the population.

Programs like VITAL 3.0 (Voluntary Incidental Trace Allergen Labelling) help manufacturers calculate this risk. If the potential cross-contamination exceeds the ED01 threshold, a "May contain" label is applied.

However, because VITAL is voluntary, many companies just slap a "May contain" label on everything to avoid lawsuits, without actually measuring the risk. This leads to "label fatigue," where consumers start ignoring warnings because they seem ubiquitous.

Decoding the Different Wordings

You’ve probably seen a dozen variations of this warning. Is "processed in a facility" safer than "may contain"? Let’s break it down.

Wording	What It Usually Means	Risk Level
"May contain peanuts"	The allergen is not an ingredient, but cross-contact is likely.	High
"Processed on shared equipment with..."	The same machinery is used. Cleaning protocols are in place, but risk remains.	High
"Made in a facility that also processes..."	The allergen is in the building. It might be on a different line, or the same one.	Moderate to High
"Not suitable for X allergy sufferers"	A direct warning often used in the UK/EU.	High

Key Takeaway: Research shows that there is no significant difference in risk between these different phrases. A product saying "Made in a facility" can contain just as much allergen residue as one saying "May contain." Do not assume one is safer than the other.

The "Russian Roulette" of Cross-Contamination

Is the risk real, or is it just a cover-your-back tactic?

Studies have shown that the risk is very real. A 2014 study found that dark chocolate with "may contain milk" warnings often contained detectable levels of milk protein—sometimes enough to cause a reaction in sensitive individuals.

Conversely, another study might find that 90% of "may contain" products have no detectable allergens. The problem is, you cannot know which category your snack falls into. It’s effectively a game of Russian Roulette. One batch might be safe, while the next batch—produced on a day when the cleaning crew was rushed—might trigger anaphylaxis.

Real Life Scenarios: Risk Assessment

Here is how to apply this knowledge in the grocery store.

Scenario A: The "Vegan" Cookie

You see a cookie labeled "Certified Vegan." You have a milk allergy. Is it safe?

• Verdict: Check the label. Vegan means no animal ingredients were intentionally added. It does not guarantee the absence of cross-contamination. Many vegan products carry a "May contain milk" warning because they are made on shared dairy lines.

Scenario B: The "Peanut-Free" Claim

A granola bar says "Peanut-Free" on the front, but "Made in a facility that processes walnuts" on the back. You have a peanut allergy.

• Verdict: Likely Safe. If a product makes a "Free-From" claim (e.g., Peanut-Free), the manufacturer usually tests to ensure it is below a certain threshold. However, the walnut warning is still relevant if you are also allergic to tree nuts.

When Is It Safe?

There are rare exceptions where you might decide to eat these products, but this should only be done under the guidance of a medical professional.

• Food Intolerance: If you are lactose intolerant (digestive issue) rather than allergic to milk protein (immune issue), small traces from cross-contamination might not bother you.
• Oral Food Challenge: Your allergist might determine your specific threshold is high enough to tolerate traces.

Emergency Plan: If You React

If you accidentally consume a product with hidden allergens, act fast.

1. Recognize Symptoms: Hives, swelling of lips/tongue, difficulty breathing, repetitive vomiting.
2. Use Epinephrine: If you have an EpiPen or Auvi-Q, use it immediately. Do not wait to see if it gets worse.
3. Call 911: Anaphylaxis can have a "biphasic" reaction, meaning it can come back hours later. You need medical observation.

How NoAllergen Helps

Reading fine print is exhausting, and "may contain" warnings are often hidden in folded corners or printed in low-contrast text.

The NoAllergen App uses AI to scan the entire package—not just the ingredient list. It specifically looks for precautionary labeling and flags it based on your profile.

• If you scan a cookie and it says "May contain nuts," NoAllergen will alert you with a DANGER or WARNING screen, ensuring you don't miss that critical safety information.

Download NoAllergen today to shop with confidence and catch hidden risks instantly.

Conclusion

The "may contain" label is frustrating, limiting, and confusing. But until laws change to require standardized, threshold-based labeling, it is the only tool we have to identify cross-contamination risks.

For the safety of yourself or your child, the best practice is to take the warning seriously. No snack is worth a trip to the emergency room.

References

1. Guidance on 'May Contain' Labelling - High Speed Training
2. Allergy Thresholds and 'May Contain' Warnings - Anaphylaxis UK
3. Food Allergy Experts on Global 'May Contain' Labels - Allergic Living
4. Precautionary Allergen Labelling Guidance - Food Standards Agency (UK)
5. Quantitative risk assessment of UK food products cross-contaminated with allergens - PubMed
6. VITAL 3.0 Guide - Allergen Bureau