What are the most common food allergens?

In the US, nine foods cause the great majority of food-allergy reactions: milk, eggs, peanuts, tree nuts, soy, wheat, fish, shellfish, and sesame. Peanuts, tree nuts, milk, and sesame tend to cause the most severe reactions. By law these nine must be clearly listed on packaged-food labels.

How can I tell a mild reaction from a dangerous one?

Mild-to-moderate reactions often look like hives, an itchy rash, swelling, vomiting, or stomach upset. Anaphylaxis is a severe, whole-body reaction with signs like trouble breathing or wheezing, swelling of the tongue or throat, repeated vomiting, pale or floppy/lethargic behavior, or fainting. Anaphylaxis is an emergency: give epinephrine immediately if prescribed and call 911.

Should I delay giving my baby peanuts and eggs?

No — current guidance flipped the old advice. The NIAID guidelines and the AAP say introducing common allergens like peanut and egg in age-appropriate forms starting around 6 months (and, for high-risk infants, sometimes as early as 4–6 months under medical guidance) actually lowers the risk of developing those allergies. Delaying does not help and may increase risk.

What's the difference between a food allergy and a food intolerance?

A food allergy involves the immune system and can be life-threatening (think peanut allergy causing anaphylaxis). A food intolerance, like lactose intolerance, does not involve the immune system; it causes discomfort such as gas, bloating, or diarrhea but is not dangerous in the same way. Only an allergy carries anaphylaxis risk.

When should I see a doctor about a suspected food allergy?

If your child has any severe reaction — trouble breathing, swelling of the lips or tongue, or sudden lethargy — call 911. For milder but repeated reactions to a food, stop giving that food and talk to your pediatrician, who may refer you to an allergist for testing. Don't start cutting out major foods long-term without medical advice.

Food allergies in babies and toddlers

The first time you hand your baby a smear of peanut butter or a bite of scrambled egg, there's often a tiny held breath: what if they react? It's a fair worry — and also one that, handled well, shouldn't keep nutritious foods off the high-chair tray. In fact, the science on baby food allergies has done a near-complete U-turn in the last decade, and the modern advice is more reassuring (and more proactive) than the cautious rules many of us grew up with.

Here's what the major allergens are, how to recognize a reaction and tell the scary kind from the manageable kind, why early introduction is now the recommendation, and how to read a label without a magnifying glass.

Food allergies in babies and toddlers: the common allergens, signs of a reaction, and why early introduction lowers risk

The usual suspects: the common allergens

A huge share of food-allergy reactions trace back to a short list of foods. By US law, nine major allergens must be declared on packaged food, per the FDA:

Milk
Eggs
Peanuts
Tree nuts (walnuts, almonds, cashews, pistachios, pecans, and others)
Soy
Wheat
Fish
Shellfish (crustaceans like shrimp and crab)
Sesame (added as the ninth major allergen in 2023)

The AAP notes that peanuts, tree nuts, milk, and sesame tend to cause the most severe reactions. Most childhood allergies to milk, egg, soy, and wheat are eventually outgrown; peanut, tree nut, fish, and shellfish allergies are more likely to last into adulthood — though every child is different.

Allergy vs. intolerance: not the same thing

People use "allergic" loosely, but the distinction is important and not just semantic. Per the AAP:

A food allergy involves the immune system. The body mistakes a harmless food protein for a threat and mounts a defense — which is what can, in the worst case, become anaphylaxis.
A food intolerance does not involve the immune system. Lactose intolerance, for example, is the gut struggling to digest milk sugar. It can cause real misery — gas, bloating, cramps, diarrhea — but it is not life-threatening and carries no risk of anaphylaxis.

Why it matters: a true allergy may call for strict avoidance and an epinephrine plan; an intolerance usually means adjusting amounts or finding a swap. Lumping them together can lead to either needless fear or dangerous complacency. When in doubt, your pediatrician can help sort which is which.

What a reaction looks like — and when it's an emergency

Most reactions show up fast, usually within minutes to a couple of hours of eating the food. The crucial skill is telling a mild-to-moderate reaction from anaphylaxis, because the response is completely different.

Mild to moderate reactions, per the AAP, can include:

Hives or an itchy rash
Swelling (often lips or face)
Vomiting, nausea, stomach pain, or diarrhea
Sneezing, a runny nose, or mild congestion

Anaphylaxis is a severe, rapidly progressing, whole-body reaction — a medical emergency. The AAP's anaphylaxis guidance describes warning signs such as:

Trouble breathing, wheezing, coughing, or a tight throat
Swelling of the tongue or throat, or trouble swallowing
Repeated vomiting alongside other symptoms
Pale, bluish, floppy, or unusually sleepy/lethargic behavior — especially important in babies, who can't tell you they feel awful
Dizziness or fainting

If you see signs of anaphylaxis, this is what to do: give epinephrine immediately if your child has been prescribed an auto-injector or nasal spray, then call 911. Epinephrine is the only first-line treatment for anaphylaxis — antihistamines like Benadryl are not a substitute and do not stop a severe reaction. The AAP advises that anyone who has had an allergic reaction to food keep two doses of epinephrine on hand, because a second dose is sometimes needed before help arrives. Even if symptoms improve after epinephrine, your child still needs to be seen, because reactions can return.

If your child has a diagnosed food allergy, ask your pediatrician or allergist for a written Allergy and Anaphylaxis Emergency Plan so every caregiver knows exactly what to do.

The big reversal: introduce allergens early, not late

For years the advice was to delay allergenic foods, on the theory that a less mature system was safer kept away from them. Research showed the opposite. The landmark evidence — reflected in the NIAID food allergy guidelines and echoed by the AAP — is that introducing common allergens early actually reduces the chance of developing an allergy. Delaying doesn't protect, and may raise risk.

The clearest example is peanut. The NIAID peanut addendum guidelines lay out an evidence-based approach:

Most babies: introduce age-appropriate peanut foods around 6 months, once they've started solids, alongside other foods.
Higher-risk babies (severe eczema and/or an existing egg allergy): talk to your doctor about introducing peanut as early as 4–6 months, sometimes after allergy testing or a supervised in-office feeding.

Practical pointers for introducing any allergen at home:

Never give whole peanuts, nuts, or globs of nut butter — those are choking hazards. Use thinned smooth peanut butter (stirred into water, breast milk, or a puree), or an age-appropriate peanut puff that dissolves.
Offer one new allergen at a time, a few days apart, so you can connect any reaction to the right food.
Do it earlier in the day when you can watch your baby for a couple of hours, not right before bed.
Once a food is tolerated, keep it in the rotation. Regular exposure is part of what maintains tolerance.

This fits hand-in-glove with the general AAP advice on starting solids around 6 months, when your baby shows readiness signs. If your family has a strong history of food allergy, or your baby has significant eczema, check with your pediatrician on timing before you start — but the default is introduce, don't avoid.

Reading labels without losing your mind

Once your child has a known allergy, the food label becomes your best friend — and US law makes it readable. Under FALCPA, any of the nine major allergens in a packaged food must be named in plain English, either:

In the ingredient list in parentheses — e.g., "lecithin (soy)," "whey (milk)" — or
In a "Contains" statement right after the ingredients — e.g., "Contains: Wheat, Milk, Soy."

A few real-world notes:

Read the label every single time, even on a product you buy weekly. Manufacturers change recipes without warning.
"May contain" and "made in a facility with" statements are voluntary, not regulated the same way. If your child's allergy is severe, treat these cautions seriously and ask your allergist how strictly to avoid them.
The law doesn't cover everything. Per the FDA, it doesn't apply to fresh produce, most foods served at restaurants and counters without packaging, or certain products regulated elsewhere. For unpackaged and restaurant food, ask directly.

If you suspect an allergy

Think your child reacted to something? Here's the calm version of what to do:

For any severe reaction — trouble breathing, swelling of the lips or tongue, repeated vomiting, or sudden floppiness — give epinephrine if prescribed and call 911. Don't wait to "see if it passes."
For a mild, isolated reaction, stop offering that food and note exactly what happened — the food, the amount, the symptoms, and how long after eating they appeared. That record is gold for your doctor.
Call your pediatrician. They can help decide whether it was likely an allergy, an intolerance, or a coincidence, and may refer you to an allergist for testing.
Don't eliminate major foods long-term on your own. Cutting out a whole food group can backfire nutritionally — and, given the early-introduction evidence, unnecessarily. Let testing guide it.

The headline to carry away: food allergies are real and occasionally serious, but the modern playbook is empowering. Introduce the common allergens early and regularly, learn the difference between hives and a breathing emergency, keep epinephrine close if your child needs it, and read the label every time. That combination handles the vast majority of situations — and lets that first bite of peanut butter be a milestone instead of a standoff.

This article is educational and not medical advice. Always check with your pediatrician, allergist, or provider, and call 911 for any breathing difficulty or severe reaction.