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Nutrition8 min readApril 2026

The 9 Major Allergens: When and How to Introduce Each One to Your Baby

Early introduction reduces allergy risk by up to 80%. Here's a practical, research-backed guide to introducing every major allergen safely — and what to watch for along the way.

Why Early Introduction Matters

For decades, parents were told to delay allergenic foods until age 1 or later. That advice was wrong. The LEAP study (2015), published in the New England Journal of Medicine, changed everything: early introduction of peanuts to high-risk infants reduced peanut allergy by 81%.

The EAT study (2016) expanded this finding across multiple allergens. Infants who were introduced to six allergenic foods from 3 months of age had significantly lower rates of food allergy compared to those who followed standard guidelines. The evidence was so compelling that the American Academy of Pediatrics (AAP) now recommends introducing allergenic foods early — around 4-6 months — rather than delaying them.

The CDC echoes this guidance: introduce potentially allergenic foods at the same time as other solid foods, not later.

Before You Start: Signs of Readiness

Don't introduce any solids — allergenic or otherwise — until your baby shows these readiness signs, typically around 4-6 months:

  • Can sit with support and has good head control
  • Shows interest in food (reaching, opening mouth)
  • Has lost the tongue-thrust reflex (doesn't push food out automatically)
  • Can move food to the back of the mouth and swallow

If your baby has severe eczema or a known food allergy, talk to your pediatrician before starting. These babies are at higher risk but also benefit most from early introduction — the LEAP study was built around exactly this population.

The Golden Rules of Allergen Introduction

1.

One new allergen at a time. Wait 2-3 days before introducing the next so you can identify the source of any reaction.

2.

Start small. Begin with a tiny amount — about 1/4 teaspoon — and increase gradually over the session if no reaction occurs.

3.

Introduce early in the day. Offer new allergens in the morning or early afternoon so you can monitor for reactions during waking hours.

4.

Keep offering it. Once safely introduced, serve each allergen 2-3 times per week to maintain tolerance. Consistency matters.

All 9 Major Allergens: Your Introduction Guide

The FASTER Act of 2021 established nine major food allergens in the United States. Here's how to introduce each one safely.

1. Peanuts

When: 4-6 months (the AAP recommends as early as 4 months for high-risk babies with severe eczema).

How: Mix a small amount of smooth peanut butter with warm water or breast milk/formula to create a thin paste. Never give whole peanuts or chunky peanut butter — they're a choking hazard. Peanut puff snacks designed for babies are another good option.

Why it matters: Peanut allergy is one of the most common and severe food allergies. The LEAP study showed that early introduction reduced allergy risk by 81% in high-risk infants.

2. Eggs

When: 4-6 months.

How: Start with well-cooked scrambled egg. The EAT study used a small amount of hard-boiled egg, mashed and mixed into puree. Always cook eggs thoroughly — raw or undercooked egg carries both allergy and food safety risks for babies.

Note: Introduce both the white and yolk. Most egg allergens are in the white, but the yolk contains some too. Offering the whole egg covers all bases.

3. Cow's Milk (as an ingredient)

When: 4-6 months (as a food ingredient, not as a drink).

How: Mix a small amount of plain whole-milk yogurt or soft cheese into purees. Do not give cow's milk as a primary drink before 12 months — it doesn't have the right nutrient balance for infants. But as a food ingredient for allergen exposure, it's safe and recommended from 4-6 months.

4. Tree Nuts

When: 6 months.

How: Thin tree nut butter (almond, cashew, walnut) mixed with warm water or puree. Never give whole or chopped nuts — they are a choking hazard until age 4+. You don't need to introduce every tree nut individually, but be aware that tree nut allergies can be specific to certain nuts. Start with one (almond butter is a common choice) and expand from there.

5. Wheat

When: 4-6 months.

How: Offer iron-fortified infant cereal made with wheat, small pieces of soft bread or toast strips, or cooked pasta cut into small pieces. Wheat is one of the easier allergens to introduce because it's in so many common baby foods.

6. Soy

When: 4-6 months.

How: Offer silken tofu (mashed or pureed), or mix a small amount of soy-based formula into food. Edamame can work for older babies (6+ months) if mashed or pureed. Avoid whole edamame beans as a choking hazard.

7. Fish

When: 6 months.

How: Start with mild, low-mercury fish like salmon, cod, or tilapia. Cook thoroughly, remove all bones, and flake into tiny pieces or mash into puree. Fish is also an excellent source of omega-3 fatty acids and DHA, which support brain development.

Safety note: The FDA recommends choosing lower-mercury options. Avoid shark, swordfish, king mackerel, and tilefish for babies.

8. Shellfish

When: 6-9 months.

How: Start with well-cooked shrimp or crab, finely minced or pureed. Shellfish allergies are more common in adults than infants, but early introduction is still recommended. Cook shellfish thoroughly — never serve raw or undercooked shellfish to babies.

9. Sesame

When: 6 months.

How: Thin tahini (sesame seed paste) mixed into puree or yogurt is the easiest method. You can also sprinkle a small amount of ground sesame seeds onto food. Avoid whole sesame seeds, which are a choking hazard. Sesame was added as the 9th major allergen by the FASTER Act of 2021, effective January 2023.

Quick Reference: Introduction Timeline

Allergen Introduction by Age

4-6 monthsPeanuts, eggs, cow's milk, wheat, soy
6 monthsTree nuts, fish, sesame
6-9 monthsShellfish

Signs of a Reaction: What to Watch For

Most allergic reactions happen within minutes to 2 hours of eating a food. Know the difference between mild and severe reactions.

Mild Reactions (monitor at home, call pediatrician)

  • Hives or red, blotchy skin
  • Redness or slight swelling around the mouth
  • Mild vomiting (one episode)
  • Increased fussiness or discomfort
  • Runny nose or sneezing after eating

Severe Reactions — Call 911 Immediately

  • Difficulty breathing, wheezing, or persistent coughing
  • Swelling of the face, tongue, or throat
  • Sudden paleness or limpness
  • Repeated vomiting
  • Loss of consciousness

Severe reactions (anaphylaxis) are rare in first exposures but can happen. If your baby has been diagnosed with severe eczema or has a known food allergy, your pediatrician may recommend having infant-dosed epinephrine (EpiPen Jr) on hand during introductions.

Common Mistakes to Avoid

  • Waiting too long. The old advice to delay allergens until 12+ months actually increased allergy rates. Earlier is better (after 4 months with readiness signs).
  • Introducing and then stopping. A single exposure isn't enough. You need consistent, regular exposure (2-3 times per week) to build and maintain tolerance.
  • Skipping allergens because of family history. Babies with a family history of allergies benefit the most from early introduction — they're the population the LEAP study proved it works for.
  • Giving unsafe forms. Whole nuts, chunks of cheese, and raw egg are choking hazards. Always use age-appropriate preparations: thin pastes, purees, finely ground, or well-cooked and mashed.

Track every allergen introduction with LilSense

LilSense's allergen tracking lets you log each new food, record reactions, and keep a clear history of what's been introduced. When you're juggling 9 allergens across weeks of introductions, having it all in one place makes the difference between confidence and guesswork.

Download Free on iOS

Frequently Asked Questions

When should I start introducing allergens to my baby?

Current guidelines from the AAP and WHO recommend introducing allergenic foods around 4-6 months of age, when your baby shows signs of readiness for solids. The LEAP study showed that early introduction of peanuts reduced allergy risk by up to 81% in high-risk infants. Don't wait until after 12 months — the research is clear that earlier is better.

Should I introduce one allergen at a time?

Yes. Introduce one new allergen at a time, waiting 2-3 days before adding the next. This makes it easier to identify which food caused a reaction if one occurs. Once an allergen has been safely introduced, continue offering it regularly — at least 2-3 times per week — to maintain tolerance.

What are the signs of an allergic reaction in a baby?

Mild reactions include hives, redness around the mouth, slight swelling of the lips, vomiting, or increased fussiness. Severe reactions (anaphylaxis) include difficulty breathing, wheezing, widespread swelling of the face, tongue, or throat, sudden paleness or limpness, and loss of consciousness. Call 911 immediately for any severe reaction.

Do I need to delay allergen introduction if my baby has eczema?

No — in fact, babies with eczema benefit the most from early introduction. The LEAP study specifically studied high-risk infants with severe eczema and found dramatic reductions in allergy risk. The AAP recommends introducing peanut-containing foods as early as 4-6 months for these babies, ideally after consultation with a pediatrician.

Is sesame now considered a major allergen?

Yes. The FASTER Act of 2021 added sesame as the 9th major food allergen in the United States, effective January 1, 2023. Sesame must now be declared on food labels. Sesame allergy affects approximately 0.23% of US children and adults, and reactions can be just as severe as other major allergens. Introduce it the same way as other allergens — thin tahini mixed into puree is the easiest method.

The Bottom Line

The science has shifted dramatically. Early, consistent introduction of allergenic foods — starting around 4-6 months — is one of the most effective things you can do to reduce your baby's risk of developing food allergies. The key is starting at the right time, using safe preparations, watching for reactions, and maintaining regular exposure.

It can feel overwhelming to track 9 different allergens across weeks of introductions. Write it down, use an app, do whatever helps you stay organized. What matters is that you start, stay consistent, and know the signs to watch for.

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