Allergen introduction: when and how to start

The advice on this changed direction completely. Parents who had older children a decade ago were told to hold allergens back; the guidance now says the opposite. If you have heard both, the newer version is the one supported by trial evidence.

Early, not late

The LEAP trial randomised 640 infants at high risk of peanut allergy — those with severe eczema, egg allergy, or both — to either eat peanut regularly from between four and eleven months, or avoid it until five years old.[3]

Follow-up found the protection lasted into adolescence, did not affect how long or how often those infants breastfed, and did not affect growth. That result is why US guidance now recommends introducing peanut in the first year rather than delaying it.[3]

UK guidance reaches the same place from the other direction: delaying peanut and hen's egg beyond six to twelve months may increase the risk of becoming allergic to them.[1]

Start when solids are established

Allergens go in after your baby has started solids and tolerated a few first foods — generally from around six months, and not before seventeen weeks. There is no advantage in making an allergen the very first thing your baby eats.[1]

How to introduce one

The form matters as much as the food

Every allergen has a version that is safe for a baby and a version that is a choking hazard. The allergen advice and the choking advice have to be followed at the same time.

• Peanut — thinned peanut butter stirred into yogurt or purée, or a peanut puff. Never whole peanuts, which stay off the menu until five.[1]
• Tree nuts — almond butter and other smooth nut butters, thinned. Ground or flaked nuts, never whole.
• Egg — well-cooked egg. Raw or lightly cooked egg is a separate food-safety question.[1]
• Cow's milk — as yogurt or cheese in food from six months. Cow's milk as a main drink waits until twelve months.
• Sesame, soy, wheat, fish and shellfish — introduced the same way, in an age-appropriate texture.

What a reaction looks like

Most reactions are mild: redness or hives around the mouth, a rash, some vomiting. These usually appear within minutes and up to two hours after eating.[1]

Cow's milk allergy can behave differently, with symptoms taking up to three days to appear and looking more like reflux, eczema or unsettled digestion than a classic allergic reaction.[1]

This is not the milk ladder

Introducing an allergen to a baby who has never reacted to it is a different thing from reintroducing a food to a child with a diagnosed allergy. The milk ladder, the egg ladder and protocols like them are for the second situation, and they belong under the supervision of an allergist or a paediatric dietitian.

If your child has a diagnosed allergy, follow the plan your specialist gave you rather than anything on this page.

A reasonable order

There is no evidence that one sequence beats another, so the order below is about practicality: the two with the strongest trial evidence first, then the rest as they fit into meals you are already making.

• Weeks 1–2 — establish a few non-allergenic first foods.
• Weeks 3–4 — peanut, then egg. These are the two with the clearest evidence behind early introduction.[4]
• Weeks 5–8 — cow's milk (in food), then wheat, then soy.
• Weeks 9+ — sesame, tree nuts, fish, then shellfish.

Once each one is tolerated, keep it in the diet regularly. This schedule is a default, not a prescription — a baby who is already eating a food happily does not need to wait for its week.