From the YummyYucky team, founded by Nancy Nash

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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 (about 3 days, since a few reactions are delayed) 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.

🛒 Our pick Don’t want to buy nine different foods? An early-allergen introduction kit doses the common allergens in pre-measured amounts, which some parents find simpler to work through. See allergen intro kits → (affiliate link: if you buy through it we may earn a little, at no cost to you; we only suggest things we'd actually use)

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 or welts, unless they are only around the mouth with nothing else
Swelling of the lips, face, or eyes
Vomiting
A change in behavior, like becoming very unsettled
If any of these show up soon after a food, stop that food and get medical advice right away
Call emergency services right away for swelling of the tongue, swelling or tightness in the throat or trouble swallowing, difficult or noisy breathing, wheezing, a cough that keeps going, or a hoarse voice
Also call emergency services for swelling of the lips or face that comes on suddenly or keeps spreading, vomiting that repeats, hives that spread over the body, skin or lips that turn pale or blue, a baby who goes floppy or is hard to wake, or signs in more than one part of the body, like hives plus vomiting

Guides for each of the big 9

Peanut

Egg

Milk (dairy)

Tree nuts

Soy

Wheat

Fish

Shellfish

Sesame

Know your big 9: how common, outgrowing it, and cross-reactivity

General, sourced background, not medical advice, and not based on your baby's logs. Cross-reactivity in particular is a conversation for your allergist, who decides what is right for your child.

Peanut

How common: About 2% of US children have a peanut allergy, the most common food allergy in kids. (FARE)
Outgrowing it: It lasts in about 3 in 4 children who have it, while most children outgrow a milk or egg allergy. (ASCIA)
Cross-reacts with: Peanut is a bean, not a tree nut, and a peanut allergy does not by itself mean a tree nut allergy. But about 40% of children with a tree nut allergy also react to peanut, so ask your allergist which nuts to test. (FARE)

Full peanut guide →

Tree nuts

How common: More than 2% of US children are allergic to one or more tree nuts (walnut, cashew, almond, pistachio, pecan, and others). (FARE)
Outgrowing it: Only about 9% of children outgrow a tree nut allergy, so it is usually lifelong. (FARE)
Cross-reacts with: Tree nuts often react together: about two-thirds of people allergic to cashew also react to pistachio, and about two-thirds allergic to walnut also react to pecan. Do not assume any single nut is safe without asking your allergist. (FARE)

Full tree nuts guide →

Egg

How common: About 2% of children are allergic to egg. (FARE)
Outgrowing it: Most children outgrow it: around 71% are no longer allergic by age 6. (FARE)
Cross-reacts with: If your child reacts to chicken egg, eggs from other birds (duck, goose, turkey, quail) may react too, so check with your allergist before trying them. (FARE)

Full egg guide →

Cow's milk

How common: About 2.5% of children under age 3 are allergic to cow’s milk. (FARE)
Outgrowing it: Most children outgrow it, around 80% by age 3 to 5, though it can last for life. (ASCIA)
Cross-reacts with: Most people allergic to cow’s milk are also allergic to other animal milks, like goat’s and sheep’s milk, so these are not safe swaps. Ask your allergist which milk to use instead. (ASCIA)

Full cow's milk guide →

Soy

How common: About 0.4% of US infants and young children are allergic to soy. (FARE)
Outgrowing it: Most children outgrow it: in one allergy-clinic study, about half had outgrown it by age 7 and about 7 in 10 by age 10. (research study)
Cross-reacts with: Soy is a legume, but most people with a soy allergy can still eat other legumes like chickpeas, kidney beans, and lentils, so ask your allergist before cutting them. Peanut is different: in one allergy-clinic study, most children with a soy allergy also had a peanut allergy, so ask your allergist how to introduce peanut. (ASCIA) (research study)

Wheat

How common: Wheat allergy affects up to about 1% of children, and is most common in young kids. (FARE)
Outgrowing it: Most children outgrow it: about two-thirds are no longer allergic by age 12. (FARE)
Cross-reacts with: A wheat allergy usually does not mean other grains are off-limits, and it is not the same thing as celiac disease. Ask your allergist which grains are safe. (FARE)

Fish

How common: Up to about 1% of people report a finned-fish allergy, and roughly 40% first react as adults. (FARE)
Outgrowing it: A fish allergy usually lasts. Only about 1 in 5 people outgrow a seafood allergy with time. (ASCIA)
Cross-reacts with: More than half of people allergic to one fish react to other fish too, so allergists often advise avoiding all fish until testing says otherwise. Fish and shellfish allergies are separate, so one does not mean the other. (FARE)

Full fish guide →

Shellfish

How common: About 2% of people report a shellfish allergy, and roughly 60% first react as adults, one of the most common adult-onset food allergies. (FARE)
Outgrowing it: A shellfish allergy is usually lifelong. (FARE)
Cross-reacts with: Allergy to one crustacean (shrimp, crab, lobster) usually means avoiding all of them. People allergic to crustaceans may tolerate mollusks (clams, oysters, scallops), but only allergy testing with an allergist can confirm that. (ASCIA)

Full shellfish guide →

Sesame

How common: About 0.2% of people (roughly 1 in 400) have a sesame allergy, the 9th most common food allergy in the US. (FARE)
Outgrowing it: Some children outgrow it (studies vary, roughly 20 to 30%), but it more often persists, like peanut or tree nut. (research review)
Cross-reacts with: Sesame overlaps with other allergies: about 40% of people allergic to sesame also react to peanut, and about 40% to at least one tree nut. Ask your allergist about testing those too. (research review)

Full sesame guide →

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.

Why space new allergens a few days apart?

Introduce one new allergen at a time and let its watch window pass (about 3 days, since a few reactions are delayed) 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. The situations that genuinely change the plan are about your baby, not the family tree: severe eczema or an existing food allergy (especially a previous immediate reaction) are the reasons to make the introduction plan with your pediatrician or allergist rather than starting on your own. Family history, even a parent with a serious allergy, is a reason to mention it at a checkup, not a reason to delay.

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, and those symptoms have many possible causes, so talk to your pediatrician before cutting foods from your diet; if they suspect a milk-protein sensitivity they may suggest a short, time-limited dietary trial followed by reintroduction to confirm it. Plan the baby’s own 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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Let the app track the big 9 for you

Log a first taste and YummyYucky opens a watch window on that allergen, tells you when it is clear to start the next, and keeps the ones that go fine in rotation. Free.

Start the allergen tracker, free

Last updated September 2026. Next review December 2026. How we write these: built from current published guidance from the AAP, CDC, FDA/EPA, NIAID, WHO, and other pediatric and public-health authorities, with sources cited on the page. See our editorial and medical policy for how we research, source, and update these, and how we double-check the food advice.

This is general information, not medical advice, and is not individualized 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.