Introducing allergens: when to start and what to offer

If you have a parent or an older sibling who was told to keep peanut away from a baby until they were three, you are holding two sets of advice that contradict each other. The newer one is not a softening of the older one. It is a reversal, and it is worth knowing that before you stand in a kitchen deciding what to do.

The advice reversed, and why

Delaying allergenic foods used to be standard caution. It is now the thing both bodies warn against.

• The NHS: evidence has shown that delaying the introduction of peanut and hen’s eggs beyond six to twelve months may increase the risk of developing an allergy to these foods.
• The AAP: there is no evidence that delayed introduction of allergenic foods like egg, peanut, dairy and sesame prevents allergies.

So the instinct to be careful by waiting now points the wrong way. Being careful looks like introducing these foods deliberately, early, one at a time, and then keeping them there.

When to start

At around six months, alongside the other first foods. The NHS phrasing is that when you start introducing solid foods from around six months, you introduce the foods that can trigger allergic reactions one at a time so that you can spot any reaction.

There is no queue to work through. Allergens are not a later stage of weaning that comes after vegetables have been mastered — they belong in the same few weeks. If you are still deciding how to start solids at all, that is covered in starting solids.

The foods that need introducing

The NHS names these as the foods that can trigger allergic reactions:

How to introduce one

• One new allergen at a time. If two arrive together and something happens, you have learned nothing usable.
• A small amount first. A taste rather than a portion, with the rest of a meal they already accept.
• At home, earlier in the day. Not on the way out, not at bedtime, and not somewhere you cannot watch them for the next couple of hours.
• Wait a couple of days before the next new one. Ordinary foods can carry on in the meantime; it is only the new allergen that is being isolated.
• Write down what and when. Reactions get argued about later, and a date beats a memory.

Serving each one safely

Most of what goes wrong here is not allergy. It is texture, and it is preventable:

• Never whole nuts. The AAP says not to feed whole peanuts or tree nuts to babies or young children because they are choking hazards, and puts the age for whole nuts at usually at least four years — old enough to be relied on to chew them well.
• Peanut, thinned. The AAP describes mixing and thinning a small amount of peanut butter into cereal, pureed fruit or yogurt. Peanut butter straight from the jar on a spoon is thick enough to be a hazard in itself.
• Seeds ground. The NHS asks for seeds, sesame particularly, to be served finely ground. Tahini thinned into something else works.
• Egg and shellfish cooked through. Eggs without a red lion stamp are not for raw or light cooking, and shellfish is not served raw or lightly cooked.

Keeping them in the diet

This is the half that gets forgotten, and skipping it undoes the work. The NHS puts it directly: once introduced and if tolerated, these foods should become part of your baby’s usual diet to minimise the risk of allergy.

The AAP frames the amount in developmentally appropriate portions — two teaspoons of peanut butter is the example it gives — kept up routinely rather than offered once and dropped.

In practice that means peanut in some form a couple of times a week rather than once in February, and egg as an ordinary part of the week rather than a test that was passed. A food that leaves the diet for months can stop being tolerated.

Higher-risk babies

One group has a different timetable, and it is the only part of this page that should not be acted on without a doctor.

The AAP describes a baby who has or has had severe, persistent eczema, or an immediate allergic reaction to any food — especially a highly allergenic one such as egg — as high risk for peanut allergy. For these babies it says peanut-containing products should ideally be introduced as early as four to six months, after other solid foods have been tolerated, and that you should talk with your child’s pediatrician first.

Both halves matter. Earlier is the guidance; through your doctor is how it is meant to happen, because some of these babies are tested or introduced in a supervised setting rather than at the kitchen table.

Mild reactions, and what to do

The NHS lists these as signs of a mild allergic reaction:

• Swollen lips or face
• Red, itchy, watery eyes
• Wheezing and coughing
• A red, itchy rash
• Worsening of eczema symptoms
• Feeling or being sick, tummy pain, diarrhoea or constipation

Stop the food. The AAP’s instruction is to stop using the new food and consult your child’s pediatrician. Do not re-test it at home to be sure — that is the appointment’s job, and a second exposure is not always milder than the first.

Anaphylaxis

The NHS describes anaphylaxis as starting quickly and causing breathing problems, a swollen throat or tongue, or a raised, itchy rash, and calls it a medical emergency.

Call emergency services immediately. Do not wait to see whether it settles, do not give anything by mouth, and do not drive if you can get an ambulance instead. If adrenaline has been prescribed for your child, use it as you were shown and still call.

When to ask

Speak to your GP, health visitor or a paediatric dietitian if:

• Your baby has had any reaction to a food, however mild it looked
• Your baby has severe or persistent eczema — before starting peanut, not after
• There is a diagnosed food allergy in a parent or sibling and you are unsure how to start
• You have been avoiding a whole food group and are not sure how to reintroduce it
• Your baby is refusing textures rather than reacting to foods, which is a different problem
• You are frightened enough of a reaction that you have stopped introducing anything new

That last one is a real reason to ask rather than an admission of anything. Stalled weaning out of fear is common, it is solvable, and it is easier to unpick early than after months of a narrowing diet.