Key takeaways
- Introduce the top nine allergens around 6 months, but not before 4 months, once your baby is eating other solid foods.
- Offer one new allergen at a time at breakfast, starting with a quarter-teaspoon, and observe for at least two hours before naptime.
- Once an allergen is tolerated, keep it in the diet twice a week. A single exposure does not maintain tolerance.
For about fifteen years, the official medical advice on infant feeding was essentially: keep your baby away from peanut butter until they are practically in preschool, and cross your fingers. In 2000, the American Academy of Pediatrics told parents to delay cow's milk until age one, eggs until age two, and peanuts until age three. Over the next decade and a half, childhood peanut allergies tripled in the UK, the US, and Australia. It was one of the biggest unintended public health missteps in modern medicine.
That guidance is completely gone. Landmark clinical trials proved that hiding allergens from a baby doesn't protect them—it actually stops their immune system from learning that food is friend, not foe.
The clinical trials that rewrote the kitchen rules
The turning point was the LEAP trial (Learning Early About Peanut Allergy, published by Du Toit et al. in the New England Journal of Medicine in 2015). Researchers tracked 640 infants between 4 and 11 months who were considered high-risk due to severe eczema or egg allergy.
Half the infants avoided peanuts completely until age five. The other half ate peanut protein regularly—about six grams a week spread across three or more meals. At age five, peanut allergies were reduced by 86% among the babies who ate peanuts early compared to those who avoided them.
The subsequent EAT study (Enquiring About Tolerance, Perkin et al., NEJM 2016) looked at the general infant population across six common allergens (milk, egg, peanut, sesame, fish, and wheat). The evidence confirmed that early, regular consumption of allergenic foods is safe and builds oral tolerance.
As a result, national paediatric and allergy bodies worldwide—including the US NIAID 2017 Addendum, the Australasian Society of Clinical Immunology and Allergy (ASCIA), and the NHS Start for Life—now recommend introducing the common allergens starting around six months, but not before four months, once your baby shows developmental readiness signs.
The 9 common allergen groups
Nine food groups cause more than 90% of all documented food allergies in infants and young children:
- Cow's milk: plain whole-milk yoghurt, hard pasteurised cheese, kefir
- Hen's egg: thoroughly cooked yolk and white
- Peanut: smooth thinned peanut butter or peanut powder
- Tree nuts: almond, walnut, cashew, hazelnut, pecan, pistachio, macadamia, brazil nut
- Sesame: unsalted tahini paste or sesame flour
- Soy: silken tofu, unsweetened soy yoghurt, edamame purée
- Wheat: infant oat/wheat cereal, soft pasta, wholewheat toast soldiers
- Fish: salmon, cod, haddock (deboned and flaked)
- Shellfish: cooked prawns, shrimp, crab (finely minced)
The 5-step introduction protocol (without the panic)
Allergen introduction isn't an exam, but having a routine takes the anxiety out of it. Here is the clinical checklist stripped of jargon:
1. Establish simple solids first
Don't make peanut paste your baby's literal first bite in this world. Start complementary feeding with simple, low-allergen foods—steamed sweet potato, avocado, broccoli, or carrot—for a week or two. Let them figure out that food goes into the mouth and stays there before you add an allergen into the mix.
2. One allergen at a time
Never introduce egg and peanut on the same Tuesday morning. If your baby gets a rash thirty minutes later, you need to know which one caused it without playing detective. Keep familiar non-allergenic foods in the meal, but introduce only one new allergen.
3. The morning rule
Always offer a new allergen at breakfast or lunch. Never at 7:30 PM right before bed. Immediate allergic reactions usually happen within 30 minutes to two hours. You want your baby awake, playing on the rug where you can see their face—not asleep in a dark nursery.
4. Start with a micro-taste
For the first exposure, give about a quarter-teaspoon of the prepared allergen mixed into a familiar purée. Put it on the tip of the spoon and feed it directly into the mouth. Wait 15 to 20 minutes. If no reaction appears, offer the remainder of the normal infant portion.
5. Skip the skin smear test
Do not rub peanut butter or egg on your baby's cheek or lips to "test" for a reaction. Baby skin is sensitive, and contact with acidic food enzymes often causes local redness that will send you into a panic for no reason. Exposing broken skin to food proteins without eating them can actually increase sensitization risk. Food belongs in the mouth.
How to prepare each allergen safely
Whole nuts and giant spoonfuls of thick peanut butter are severe choking hazards. Read our guide on gagging vs choking in baby-led weaning for full texture guidance. Every allergen needs safe preparation:
- Peanut and tree nuts: Thin smooth nut butter with warm water, breast milk, or formula until it looks like runny yoghurt. Stir into warm oatmeal or fruit purée.
- Egg: Cook thoroughly. Runny or undercooked egg contains proteins that trigger reactions more readily during early exposure. Mash a hard-boiled egg yolk and white with breast milk, or slice a well-cooked omelette into finger-length strips.
- Cow's milk: Whole milk as a drink stays off the menu until 12 months because it lacks iron. Dairy solids, however—like plain whole-milk yoghurt or pasteurised cheddar—can start right at six months.
- Sesame: Mix pure unsalted tahini into vegetable purées or thin hummus.
- Fish and shellfish: Steam or bake fillets and flake with your fingers to hunt for small pin bones. Finely mince cooked prawns into soft mash.
The step most parents miss: maintaining tolerance
A single successful exposure is not a vaccine. Once a food has been tolerated, your baby's immune system needs regular exposure to keep that tolerance alive.
ASCIA guidance recommends serving each introduced allergen in your child's regular diet roughly twice a week throughout the first year. If you introduce peanut at six months and then forget to serve it again until month ten, the child can lose tolerance and develop an allergy during the break.
This is where things usually fall apart. Juggling nine allergen groups twice weekly while trying to cook dinner is tough. 100 Bites includes a dedicated nine-group allergen tracker that shows which groups you have introduced and alerts you when one hasn't been served lately.
Recognising a reaction: mild vs severe
Immediate allergic reactions (IgE-mediated) typically appear within minutes up to two hours after eating.
Mild to moderate symptoms:
- Hives or welts (raised red itchy patches on the skin)
- Swelling of the lips, face, or around the eyes
- Tingling mouth (older infants may rub their tongue or face repeatedly)
- Sudden vomiting or loose bowel movements
If these occur, stop feeding the food immediately, wash the baby's face, snap a photo of any rash or swelling for your doctor, and seek medical advice from your GP or urgent care.
Severe symptoms (Anaphylaxis):
- Difficult or noisy breathing (wheeze or persistent cough)
- Swelling of the tongue
- Pale, limp, or floppy appearance
- Loss of consciousness
Anaphylaxis is a medical emergency. Call your local emergency services (999 in the UK, 911 in the US, 000 in Australia, 112 in the EU) immediately. Lay the infant flat; do not hold them upright.
Feeding your baby should feel like an adventure, not a medical procedure. Methodical introduction, morning timing, and keeping a reliable log turns allergen introduction into just another morning breakfast. For pacing the rest of your meals, see our roadmap on 100 foods before one.
Feeding your baby shouldn't feel like an exam. 100 Bites gives you three fresh ideas every morning, tracks all nine allergen groups, and remembers what happened so you don't have to keep a mental spreadsheet at 7am.
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