How to introduce allergens to your baby

For years, parents were told to wait on allergens. The science has since flipped. Large studies — most famously the LEAP trial — found that introducing allergens like peanut early and keeping them in the diet is associated with a lower risk of developing a food allergy. U.S. NIAID guidelines (2017) and the American Academy of Pediatrics now support early, sustained introduction for most babies.

This guide walks you through the whole thing: when to start, what to offer, a sample schedule, and exactly what to watch for.

01When can you start introducing allergens?

Most babies are ready to start solids — and allergens — around 6 months, once they can sit up with support, hold their head steady, and show interest in food. For higher-risk babies (severe eczema and/or egg allergy), guidelines highlight a 4–6 month window for peanut, ideally after a chat with your doctor.

• Start when your baby is healthy — not mid-cold or teething miserably.
• Offer allergens earlier in the day so you can watch for a reaction.
• Make sure baby has already tried a few "regular" first foods without trouble.

02The 9 most common baby food allergens

In the U.S., nine foods cause most allergic reactions. You'll want to introduce each of these (in baby-safe forms) and keep the ones that go well in rotation:

• Peanut — thinned smooth peanut butter or peanut puffs
• Tree nuts — almond, cashew, walnut, hazelnut, pecan, pistachio (as thinned nut butters)
• Egg — well-cooked, scrambled or baked
• Milk — yogurt and cheese (not cow's milk as a drink until 12 months)
• Soy — tofu, edamame purée
• Wheat — iron-fortified infant cereals, well-cooked pasta
• Sesame — thinned tahini
• Fish — cooked, flaked, deboned
• Shellfish — cooked, finely chopped (often introduced a little later)

Want the deep dive on each one? Read the top 9 baby food allergens. For the nut family specifically, the tree-nut hub covers all seven.

03How to introduce allergens, step by step

1. Pick one allergen and a baby-safe form (for peanut: smooth peanut butter, never whole nuts or thick globs — those are choking hazards).
2. Thin it down. Mix a small amount into warm water, breast milk, formula, or a familiar purée until it's smooth and easy to swallow.
3. Offer a tiny taste first. Give a little on the tip of a spoon, then wait about 10 minutes. If there's no reaction, offer a bit more.
4. Watch for about 2 hours. Most reactions show up quickly. Stay home and keep an eye on your baby.
5. Keep it in the diet. Once it goes well, serve that allergen regularly — about twice a week — to help maintain tolerance.

04A simple allergen introduction schedule

There's no single "correct" order, but introducing one new allergen every few days keeps things manageable. Here's an example you can adapt:

Days	New allergen to try	Baby-safe form
1–3	Peanut	Thinned smooth peanut butter
4–6	Egg	Well-cooked scrambled egg
7–9	Tree nuts	Thinned nut butter (e.g. almond)
10–12	Milk	Plain whole-milk yogurt
13–15	Sesame	Thinned tahini
16–18	Soy & wheat	Tofu purée; iron-fortified cereal
19+	Fish, then shellfish	Cooked, flaked, deboned

What's the "3-day rule"?

The "3-day rule" (sometimes the "wait-and-watch" rule) means introducing one new food and waiting about three days before adding another new one. If a reaction appears, you'll know which food likely caused it. It's a helpful habit while you're working through allergens — but remember, once a food is tolerated you should keep offering it, not drop it.

How to spot an allergic reaction

Most reactions are mild and happen within minutes to a couple of hours.

• Mild signs: a few hives, redness around the mouth, mild swelling, an itchy rash, or a bit of vomiting. Stop the food and call your pediatrician.
• Severe signs (call 911): trouble breathing, wheezing, swelling of the lips/tongue/face, repeated vomiting, pale or floppy baby, or any sign of a whole-body reaction.

Frequently asked questions

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