Introducing Allergens to Your Baby: A Practical Guide

For about 20 years, parents were told to wait. Wait until 1. Wait until 3 for peanut. Keep allergens away from babies at all costs. Then in 2015 a trial called LEAP showed the opposite, and pediatric guidance has been catching up ever since.

The current recommendation: introduce common allergens between 4 and 6 months, as soon as your baby is ready for solids, and keep exposing them regularly. Early introduction reduced peanut allergy by 81% in high-risk infants in the LEAP trial.¹

What are the Big 9 allergens?

The US FDA (per the FASTER Act of 2021) recognizes nine foods that cause roughly 90% of food allergies: milk, eggs, fish, crustacean shellfish (shrimp, crab, lobster), tree nuts, peanuts, wheat, soybeans, and sesame.²

"Tree nuts" is a category, not one food. Almonds, cashews, walnuts, pecans, pistachios, hazelnuts, brazil nuts, macadamia, and pine nuts each need to be introduced separately. A baby tolerant to almonds can still react to cashews.

The other common allergen outside the Big 9 is kiwi, but most pediatricians focus on the nine above.

When should I start?

Around 6 months, as soon as your baby is showing readiness signs for solids (sitting up, good head control, lost tongue-thrust reflex, interest in food). Starting earlier than 4 months is not recommended.

For infants with severe eczema or egg allergy (considered high-risk), the NIAID 2017 peanut guidelines recommend introducing peanut as early as 4 to 6 months, ideally under an allergist's guidance, with possible skin-prick or blood testing first.³

For infants without those risk factors, you can introduce peanut and other allergens at home alongside other solids, starting around 6 months. The AAP 2019 update to pediatric allergy guidance explicitly reversed the old "delay until 1 year" advice.⁴

Why early introduction works

The immune system develops tolerance to proteins it's exposed to during a critical window in infancy. Skin exposure (especially through eczematous skin) can sensitize a baby to an allergen, while oral exposure teaches the immune system to tolerate it.¹ Delay means skin exposure without oral exposure, which tips the balance toward sensitization.

The EAT trial tested this on 1,303 exclusively breastfed infants. The per-protocol analysis (infants who actually ate the assigned foods) showed any-food allergy at 3 years was 2.4% in the early-introduction group vs 7.3% in the standard-introduction group.⁵ Peanut allergy was 0% vs 2.5%. Egg allergy was 1.4% vs 5.5%.

The intent-to-treat analysis was not statistically significant, which means early introduction works when parents actually do it consistently. Skipping weeks or months reduces the protective effect.

The Big 9: how to introduce each

Start with a few spoonfuls of the food in an age-appropriate form. Offer it in the morning so you can watch for reactions through the day. Wait 2 to 3 days between introducing new allergens so you can tell which one caused a reaction if something happens.

Peanut. Thinly spread smooth peanut butter on a teaspoon of oatmeal, yogurt, or banana. Never a blob of peanut butter (choking hazard) and never whole peanuts (choking hazard until age 4). Peanut puffs like Bamba work well once the baby is handling finger foods. Aim for 2 grams of peanut protein per serving, 3 times per week, based on the LEAP dosing.

Egg. Fully cooked scrambled egg or hard-boiled egg mashed with breastmilk, formula, or avocado. Start with a small amount (1/8 of an egg). Never raw or runny eggs before age 1.

Dairy. Plain whole-milk yogurt, cottage cheese, or soft cheese (not cow's milk as a drink before 12 months). Butter in cooked foods also counts.

Wheat. Iron-fortified infant cereal, thin strips of toast, small pieces of pasta.

Soy. Edamame (mashed or shelled), tofu cubes, soy yogurt.

Tree nuts. Nut butters (thinly spread, never blobs). Almond butter, cashew butter, etc. Each tree nut is its own allergen, so introduce them one at a time.

Fish. Soft cooked salmon (deboned carefully), white fish like cod. Flake into small pieces.

Shellfish. Small pieces of well-cooked shrimp once the baby handles other proteins well. Deboned and shell-free.

Sesame. Tahini thinly spread on toast, or mixed into hummus, or sprinkled sesame on a soft food.

Our food index has per-food prep notes and age-floors.

What does a reaction look like?

Most reactions happen within 2 hours of eating the allergen, often within minutes.

Mild reaction. A few hives around the mouth or on the chest. Mild swelling. Fussiness. A small amount of vomiting. Mild eczema flare-up.

Severe reaction (anaphylaxis). This is an emergency. Signs include:

• Trouble breathing, wheezing, or noisy breathing
• Swelling of the lips, tongue, or throat
• Widespread hives or rash over the body
• Pale or bluish skin
• Repeated vomiting, diarrhea
• Floppiness, unresponsiveness, loss of consciousness

Anaphylaxis typically involves symptoms from two or more body systems (for example, skin and respiratory, or skin and gastrointestinal).

What to do if you see a reaction

Mild reaction. Stop offering the food. Give an age-appropriate dose of pediatric antihistamine (ask your pediatrician about correct dosing for your baby's weight). Call your pediatrician within a day or two to discuss next steps, testing, and whether future exposure should happen under medical supervision.

Severe reaction. Call emergency services immediately (911 in the US). If your baby has been prescribed epinephrine (EpiPen Jr, Auvi-Q), use it right away. Do not wait to see if it gets worse. Do not drive to the hospital yourself. Emergency responders can administer oxygen, IV fluids, and more epinephrine on the way.

Always call 911 for suspected anaphylaxis even if the baby seems to recover. Biphasic reactions (a second wave of symptoms) can happen hours later and need to be managed in a hospital.

Keeping exposure going

The LEAP and EAT trials both emphasized regular, ongoing exposure. Introducing peanut once and then stopping does not protect long-term. Aim for each of the major allergens (especially peanut, egg, and dairy) at least once or twice per week once tolerated.

This is one of the places where tracking helps. With 9 allergens and 2-to-3-day introduction windows, it's easy to lose track of what you've offered, when, and in what form. nappi's food log flags the Big 9 and shows your introduction history so you can see gaps at a glance.

Should I have epinephrine at home?

For most babies without known risk factors, this is a conversation with your pediatrician. Families with a strong history of food allergy, severe eczema, or a confirmed allergy to one food are often prescribed an epinephrine auto-injector (EpiPen Jr or Auvi-Q, weighing below 15 kg).

If your baby reacted to one allergen, you may be referred to an allergist for testing before introducing others in the same family. That's standard care, not an overreaction.

Our post on gagging vs choking covers safe food prep that applies to all allergen introductions.

Frequently Asked Questions

Can I introduce peanut at home if my baby has eczema?

It depends on severity. Mild to moderate eczema: home introduction is generally fine around 6 months. Severe eczema, or known egg allergy: the NIAID 2017 guidelines recommend seeing an allergist first, with possible skin-prick testing, and supervised introduction if indicated. When in doubt, ask your pediatrician.

Is it safe to introduce more than one allergen at a time?

Single-allergen introduction with a 2-to-3-day wait between new foods makes it easier to identify which one caused a reaction if anything happens. Once a baby has tolerated several allergens individually, it's fine to serve them together.

Does my baby need to be breastfed for early introduction to work?

No. The LEAP trial included formula-fed babies. The EAT trial was specifically in exclusively breastfed babies. Both showed benefit from early introduction. The immune-tolerance mechanism works regardless of milk source.

What if I've already delayed past 6 months?

Not a disaster. Introduce the allergens now. Babies older than 6 months can still develop tolerance. The LEAP trial's benefit came from introduction between 4 and 11 months.

Are peanut puffs as effective as peanut butter?

Yes, if the puff is made with actual peanut. Bamba (the Israeli peanut snack used in the LEAP trial) contains about 3 grams of peanut protein per serving. Check the label: "peanut flour" or "ground peanut" as a primary ingredient, not "peanut flavor."