How to Introduce the 9 Common Allergens (and Why the Advice Reversed)

The advice on food allergens reversed within a single generation. Parents who were told to delay peanut until 3 years old are now being told to start at 6 months. That is not fashion — it is what happened when the delay hypothesis was actually tested.

What changed

For years the standard advice in several countries was to delay peanut, egg and fish, on the reasonable-sounding theory that a less mature immune system would be more likely to react badly.

Rates of peanut allergy rose anyway. Meanwhile researchers noticed that Jewish children in Israel, where a peanut snack is a common infant food, had roughly a tenth the peanut allergy rate of Jewish children in the UK, where the delay advice was being followed.

The LEAP trial put it to the test directly: infants at high risk of peanut allergy were randomised either to eat peanut regularly from infancy or to avoid it until 5. Early introduction reduced peanut allergy by around 80%.

The guidance changed. NIAID now recommends introducing peanut around 6 months for most infants, and between 4 and 6 months — with clinical involvement — for infants with severe eczema or egg allergy. The AAP’s clinical report says the same for allergenic foods generally: there is no benefit to delaying them past around 6 months.

The nine

In the United States, nine foods are recognised as major allergens:

Allergen	Easiest way in	Usually outgrown?
Peanut	Thinned smooth peanut butter	Often not
Egg	Well-cooked omelette strips	Usually
Milk	Plain full-fat yogurt	Usually
Wheat	Toast fingers	Usually
Soy	Firm tofu strips	Usually
Tree nuts	Thinned almond or cashew butter	Often not
Sesame	Thinned tahini, or hummus	Often not
Fish	Flaked salmon or cod	Rarely
Shellfish	Finely chopped shrimp	Rarely

In the EU and UK the labelling list is longer — 14 allergens, adding celery, mustard, lupin, molluscs and sulphites — but the nine above are the ones worth introducing deliberately.

How to do it

Wait until a couple of ordinary first foods have gone down without incident. You want a baseline before you introduce something with the potential to react.

One allergen at a time. If you introduce peanut and egg on the same day and something happens, you have learned nothing useful.

At home, earlier in the day. Not at nursery, not at a restaurant, not at 6pm on a Sunday. You want to be somewhere you can watch, with a health service open.

Start small. A quarter-teaspoon of thinned peanut butter is a fine first exposure. If nothing happens in fifteen minutes, offer a little more.

Watch for two hours. Most reactions appear within minutes to two hours.

Then keep it going. This is the part most families miss.

Maintenance is the whole point

A single exposure does not build tolerance. The LEAP protocol had children eating peanut regularly — around 6 g of peanut protein a week, spread across three or more feeds — for years, not once.

Current guidance is to keep each allergen in the diet roughly twice a week on an ongoing basis. An allergen introduced at 6 months and then forgotten about is not much better than one never introduced at all.

In practice that means nine foods to keep track of, each needing to appear about twice a week, over months. This is genuinely hard to hold in your head at 6am with a baby who did not sleep — which is exactly why we built the tracker in the FirstNom app, and why it exports a dated summary you can hand to your pediatrician.

A workable order

There is no official sequence. This one front-loads the allergens with the strongest evidence and the ones easiest to prepare:

1. Egg — well-cooked omelette strips. Easy, cheap, high nutritional payoff.
2. Peanut — thinned smooth peanut butter. Strongest evidence of the nine.
3. Milk — plain full-fat yogurt. Note this is dairy as a food; cow’s milk as a drink still waits until 12 months.
4. Wheat — a strip of toast.
5. Soy — firm tofu strips.
6. Sesame — thinned tahini, or home-made hummus.
7. Tree nuts — almond butter first, then cashew a few days later. They are separate proteins.
8. Fish — flaked salmon or cod, bones checked meticulously.
9. Shellfish — finely chopped cooked shrimp.

Tree nuts are a group, not one food. Almond, cashew, walnut, hazelnut, pistachio, pecan, Brazil and macadamia are distinct proteins, and tolerating one says little about the others. Most families introduce two or three of the common ones and handle the rest as they come up.

Two safety points that matter

Never serve nut or seed butter as a thick blob. Thick nut butter can adhere to the roof of the mouth and the back of the throat, and it is a genuine choking hazard. Always thin it with water, milk or yogurt until it pours, or spread it very thinly. Whole nuts stay off the menu until around 4 to 5 years.

Know what anaphylaxis looks like. Difficulty breathing, wheezing, a swollen tongue or throat, widespread hives, sudden floppiness or pallor. Call your emergency number. Do not drive to a hospital yourself — you cannot treat a deteriorating baby while driving.

When to talk to a doctor first

Do not do the first introduction unsupervised if your baby has:

• Severe or persistent eczema
• An already diagnosed food allergy
• A sibling or parent with a significant food allergy, particularly anaphylaxis

These babies still benefit from early introduction — arguably more than anyone. But the first exposure may need testing or clinical supervision, and that is a conversation to have before you open the jar, not after.