Introducing common allergens to your baby early, starting around 4 to 6 months of age, significantly lowers the chance of developing food allergies. This is a major shift from older advice that told parents to delay allergens until age one or later. The science now clearly supports the opposite approach: earlier exposure trains the immune system to tolerate these foods rather than react to them.
Why Early Introduction Matters
The landmark LEAP trial, published in the New England Journal of Medicine, tested what happened when high-risk infants ate peanut regularly versus avoiding it entirely. By age five, 13.7% of the avoidance group had developed a peanut allergy compared to just 1.9% of the group that ate peanut. That’s an 86% reduction in peanut allergy from early, consistent exposure. These results reshaped pediatric guidelines worldwide and apply broadly to other allergens as well.
When to Start
Most infants are ready for allergen introduction between 4 and 6 months, once they’ve started solid foods. Your baby should be able to sit upright with support, show interest in food, and swallow purees without pushing them back out with their tongue.
If your baby has severe eczema, an existing egg allergy, or both, the FDA recommends introducing peanut-containing foods as early as 4 months. These conditions increase the risk of peanut allergy, so earlier introduction is especially important. For babies in this higher-risk group, talk with your pediatrician first, as allergy testing before introduction may be recommended.
The Nine Major Allergens
Nine foods account for the vast majority of allergic reactions. These are the ones to introduce deliberately and track:
- Milk (cow’s milk in yogurt or cheese, not as a drink)
- Eggs
- Peanuts
- Tree nuts (almonds, walnuts, cashews, pecans)
- Soy
- Wheat
- Fish (bass, cod, flounder)
- Shellfish (shrimp, crab, lobster)
- Sesame
Together, these nine foods cause about 90% of food allergy reactions. Sesame was added to the official U.S. list in 2021. You don’t need to introduce all nine at once, but the goal is to get each one into your baby’s diet during that first year.
How to Introduce One Allergen at a Time
Introduce only one new allergen per meal. This way, if your baby has a reaction, you’ll know exactly which food caused it. Start with a small amount, around a quarter teaspoon, and watch for any signs of a reaction over the next one to two hours. If your baby tolerates it well, increase the amount at the next feeding, moving from a quarter teaspoon to a half teaspoon and gradually building from there.
Offer the new food earlier in the day rather than before bedtime, so you have plenty of time to observe your baby. Wait two to three days before introducing the next new allergen. There’s no required order, though many parents start with peanut and egg since these are among the most common childhood allergies.
Safe Ways to Prepare Peanut
Never give a baby whole peanuts, peanut chunks, or a spoonful of peanut butter. All of these are choking hazards. Instead, aim for about 2 grams of peanut protein per serving using one of these methods:
- Peanut puffs: About 21 pieces of a peanut puff snack like Bamba. For babies under 7 months, soften the puffs with 4 to 6 teaspoons of water. Older babies who handle dissolvable textures can eat them as-is.
- Thinned peanut butter: Mix 2 teaspoons of smooth peanut butter with 2 to 3 teaspoons of hot water. Stir until fully dissolved and let it cool. Add more water or some infant cereal if needed to thin it further.
- Peanut butter puree: Blend 2 teaspoons of smooth peanut butter into 2 to 3 tablespoons of a fruit or vegetable puree your baby already eats.
- Peanut flour or powder: Stir 2 teaspoons of peanut flour or peanut butter powder into about 2 tablespoons of a tolerated fruit or vegetable puree.
The key is a smooth, thin consistency that your baby can swallow easily without gagging or choking.
Safe Ways to Prepare Egg
Baked egg is the safest form for introduction. The high, sustained heat of baking breaks down the proteins most likely to trigger a reaction. Research shows that over 70% of egg-allergic children can tolerate egg baked into foods like muffins or cookies, and starting with baked egg may actually help resolve an egg allergy faster.
In clinical testing, baked egg produced a 0% reaction rate compared to 17% for heated egg yolk and 22% for egg white. A simple approach: bake a small amount of egg into a mini muffin or pancake using a recipe your baby can handle texture-wise. Once baked egg is tolerated over several feedings, you can move to well-cooked scrambled egg in small, soft pieces.
Other Allergens: Practical Tips
For tree nuts and sesame, the same thinning principle applies. Mix a small amount of almond butter, cashew butter, or tahini (sesame paste) into a puree or warm water to create a smooth, runny consistency. Wheat is easy to introduce through infant cereal or small pieces of soft bread. Soy shows up in tofu, which you can mash into a smooth texture. For fish, flake well-cooked, mild white fish into tiny soft pieces or blend it into a puree. Yogurt made from cow’s milk is one of the simplest ways to introduce milk protein.
Every food should be soft enough that you could mash it between your fingers. Avoid hard, sticky, or chunky textures until your baby is developmentally ready for them.
Keeping Allergens in the Diet
Introduction alone isn’t enough. After your baby tolerates an allergen, keep offering it regularly. Aim to include each allergen a few times per week. Consistency matters because ongoing exposure is what maintains the immune system’s tolerance. If you introduce peanut once and then don’t offer it again for months, you may lose the protective benefit of early exposure.
This doesn’t need to be complicated. Rotating through allergen-containing foods as part of normal meals works well. A little peanut butter in oatmeal one day, some yogurt the next, scrambled egg the day after. The goal is making these foods a routine part of your baby’s diet, not a one-time event.
Recognizing an Allergic Reaction
Symptoms of a food allergy typically appear within minutes to an hour after eating. Mild to moderate reactions include:
- Hives or a red, blotchy rash
- Swelling of the lips, tongue, or face
- Itching around the mouth
- Vomiting or diarrhea
- Stomach cramps
- Worsening eczema
Severe reactions (anaphylaxis) are rare but require immediate emergency attention. Signs include difficulty breathing, wheezing, throat tightness, dizziness, or sudden limpness. A mild rash on its own is common and usually not dangerous, but any breathing difficulty or combination of symptoms affecting multiple parts of the body warrants a call to emergency services.
A small red rash right around the mouth where food touched the skin is often just contact irritation, not an allergy. It typically fades on its own. True allergic hives appear as raised welts and can show up anywhere on the body, not just where the food made contact.