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Introducing allergens to your baby: the complete guide

Not long ago, parents were told to delay allergens. The science flipped. Research like the LEAP study showed that introducing allergens early and keeping them in the diet can actually reduce the chance of a food allergy developing. Here's the practical version.

1. Start around 6 months, when baby is ready

Most babies are ready for solids around 6 months, when they can sit with support, hold their head steady, and show interest in food. You don't need to introduce allergens before other foods, but you don't need to save them for last either.

2. One new allergen at a time, and let its window pass

Introduce a single new allergen on its own, and let its watch window pass (a few days) before starting the next brand-new one, so if a reaction happens you know exactly which food caused it. If two allergens are being watched at once and a reaction shows up, it is much harder to tell which one was responsible. This is not a reason to stall for weeks: introduce the common allergens early and steadily, one clean window at a time. (YummyYucky keeps each observation window for you and reminds you to keep the tolerated ones in rotation.)

3. Serve it in a safe form

Allergen foods have to be age-appropriate and choke-safe: smooth, thinned nut butters (never whole nuts), well-cooked egg, soft flaked fish with bones removed. Each allergen guide below covers the safe forms.

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4. Keep it in the diet

Introducing an allergen once isn't the finish line. Once it's tolerated, offer it regularly. That continued exposure is part of what the guidance is based on.

5. Higher-risk babies: talk to your pediatrician first

If your baby has severe eczema or an existing food allergy (especially egg), guidelines may recommend evaluation and earlier, supervised introduction of peanut. Check with your pediatrician before you start.

Signs of an allergic reaction

Hives, redness, or swelling (lips, face, tongue)
Vomiting or lots of drooling/coughing right after eating
Widespread rash or worsening eczema
Trouble breathing, wheezing, or floppiness: call emergency services immediately

Guides for each of the big 9

Peanut

Egg

Milk (dairy)

Tree nuts

Soy

Wheat

Fish

Shellfish

Sesame

Frequently asked questions

At what age should I introduce allergens to my baby?

For most babies, common allergens can be introduced around 6 months, once your baby is developmentally ready for solids. Current guidance generally favors introducing allergens early rather than delaying them. Babies with severe eczema or a known food allergy should talk to a pediatrician first.

What is the 3-day wait between allergens?

Introduce one new allergen at a time and let its watch window pass (a few days) before starting the next brand-new one, so that if a reaction happens you know which food caused it. If two allergens are being watched at once and a reaction shows up, it is much harder to tell which one was responsible. This is not a reason to delay: introduce the common allergens early and steadily, one clean window at a time.

Do I need to keep giving an allergen after the first try?

Yes, once an allergen is tolerated, current guidance is to keep it in the diet regularly rather than offering it once and stopping.

Which allergens should I introduce first?

Peanut and egg are the most studied and are often introduced early. Beyond that, you can work through the big 9 one at a time in whatever order fits your meals.

If I have a food allergy, is my baby likely to have one too?

Family history nudges the odds up, but it is not a sentence. Having a food allergy makes your baby a little more likely to have allergies in general, yet most babies whose parent has a food allergy never develop that same one. What tends to run in families is the allergic tendency (food allergy, eczema, asthma, hay fever), not one specific food. Here is the part that surprises people: higher risk is a reason not to delay the common allergens, not a reason to avoid them, since early and regular exposure is what helps build tolerance. For a higher-risk baby, though (severe eczema, an existing food allergy, a parent who has had anaphylaxis, or celiac in the family), make that introduction plan with your pediatrician or allergist rather than starting on your own.

A food I ate bothered my breastfed baby. Does that mean they are allergic to it?

Not necessarily, and often not. A food in your diet can sometimes bother a breastfed baby (extra fussiness, eczema, or mucousy or blood-flecked stool, most often from cow’s milk or soy). Many of these babies go on to eat that food directly with no trouble, but yours did show a sensitivity, so plan the direct introduction with your pediatrician or allergist instead of guessing, and watch closely the first few times. If the earlier reaction ever involved hives, swelling, or any trouble breathing, treat that as a possible true allergy and get medical guidance before offering the food again.

Sources

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Track it in YummyYucky

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Last updated July 2026. Next review January 2027. How we write these: grounded in widely published pediatric guidance (the AAP, WHO, the NIAID 2017 allergen guidelines, and the LEAP study), and pending independent review by a pediatric professional. See our editorial and medical policy for how we research, source, and update these.

This is general information, not medical advice, and has not been individually reviewed for your baby. Always talk to your pediatrician about your baby's diet, introducing allergens, and any reaction. In an emergency, contact emergency services.

Some links in our guides are affiliate links: if you buy through them we may earn a small commission, at no extra cost to you. We only suggest things we'd actually use, and it never changes our guidance.