Starting allergenic foods between 4 and 6 months of age is the most effective strategy to prevent food allergies. This is a shift from older advice that recommended delaying these foods, and it’s now backed by strong evidence. The landmark LEAP trial found that introducing peanut early reduced peanut allergy risk by 86% in infants who weren’t yet sensitized and by 70% in those who already showed early signs of sensitivity. Waiting past 10 months is associated with more than double the risk of developing a food allergy.
When to Start
Your baby should be showing signs of readiness for solid foods before you introduce any allergens. That means sitting upright with support, showing interest in food, and being able to move food from the front of their mouth to the back. For most babies, this happens around 4 to 6 months.
The AAP and the Dietary Guidelines for Americans both endorse introducing allergenic foods around 6 months, while the National Institute of Allergy and Infectious Diseases specifically recommends that babies with severe eczema or egg allergy start peanut-containing foods as early as 4 to 6 months. If your baby has severe eczema, talk to your pediatrician about whether earlier introduction and allergy testing make sense.
The Nine Major Allergens
The nine foods responsible for most allergic reactions in the U.S. are:
- Milk (cow’s milk protein, found in yogurt and cheese)
- Eggs
- Peanuts
- Tree nuts (almonds, walnuts, pecans, cashews)
- Soy
- Wheat
- Fish (bass, cod, flounder)
- Shellfish (shrimp, crab, lobster)
- Sesame
You don’t need to introduce all nine at once. Focus on one new allergen at a time so you can clearly identify the source if your baby reacts.
How to Space Out New Allergens
There’s no universally mandated waiting period between new allergens, but most pediatricians suggest waiting 2 to 3 days before introducing a different one. This window gives you enough time to spot a delayed reaction, which can show up as a rash, vomiting, or unusual fussiness, without dragging out the overall timeline too long. Allergic reactions typically appear within minutes to a couple of hours, but gut-related symptoms can take longer.
Offer the new food early in the day, ideally in the morning or at lunch. This way, if a reaction does occur, you’re awake and alert to respond rather than discovering symptoms overnight.
How to Prepare Each Allergen Safely
The biggest safety concern is choking, not the allergy itself. Whole peanuts, whole tree nuts, and large chunks of hard food are choking hazards for babies and young children. Here’s how to serve the most common allergens in age-appropriate forms.
Peanuts and Tree Nuts
Never give a baby a whole peanut or tree nut. Instead, thin a small amount of smooth peanut butter into infant cereal, pureed fruit, or yogurt. You can also dissolve peanut butter in breast milk or formula and spoon-feed it. The same approach works for cashew butter, almond butter, and tahini (sesame seed paste). Start with about half a teaspoon mixed in, and work up to roughly 2 teaspoons of nut butter per serving.
Eggs
Well-cooked egg is key. Scrambled eggs or mashed hard-boiled eggs work well. Start with about a third of an egg, mashed into a soft texture your baby can handle. Avoid runny or undercooked eggs for infants.
Dairy
This is where parents often get confused. You can introduce cow’s milk protein early through yogurt and cheese, which are fine starting around 6 months. Plain whole-milk yogurt is an easy first dairy food. However, cow’s milk as a drink should wait until 12 months. The distinction matters because milk as a beverage can displace breast milk or formula, which remains a baby’s primary nutrition source in the first year.
Wheat, Soy, Fish, and Sesame
Wheat can be introduced through soft, well-cooked pasta or infant cereal. Soy is easy to include through tofu, mashed to a smooth texture. For fish, offer small flakes of mild, well-cooked white fish like cod or flounder, checking carefully for bones. Sesame is simple: stir a small amount of tahini into a puree.
Keep Serving It After the First Taste
A single successful introduction isn’t enough. To maintain tolerance and reduce the chance of your child developing an allergy later, you need to keep each allergen in their diet regularly. The Australasian Society of Clinical Immunology and Allergy recommends offering each tolerated allergen at least once a week as part of a varied diet. For peanut and egg specifically, once-weekly exposure appears important for sustained protection.
This is where many parents fall short. It’s easy to try peanut once, check the box, and move on. But inconsistent exposure can undermine the protective benefit of early introduction. Build allergens into your baby’s normal rotation of meals: peanut butter stirred into oatmeal one morning, scrambled egg another, yogurt at lunch, fish at dinner later in the week.
What an Allergic Reaction Looks Like in Babies
Babies show allergic reactions differently than older children and adults. The most common signs are skin reactions (hives, rash, redness around the mouth), swelling, vomiting, and diarrhea. Babies are also more likely than older kids to show sudden behavioral changes, like becoming unusually irritable or limp, or developing a hoarse cry.
Mild reactions often stay limited to the skin. Localized hives around the mouth after a first taste of egg, for example, is a common pattern. This doesn’t necessarily mean your baby has a severe allergy, but it does mean you should stop offering that food and discuss next steps with your pediatrician before trying again.
A severe allergic reaction, called anaphylaxis, involves two or more body systems. In infants, this might look like hives combined with repeated vomiting, or a rash along with difficulty breathing or a hoarse cry. Signs involving the heart and blood vessels, like a blue-grey skin color or sudden loss of head control, are less common but serious. If your baby shows symptoms in more than one body system, call 911 immediately.
Babies Who Weigh Under 33 Pounds
One practical concern for parents of very young babies: epinephrine auto-injectors (the standard emergency treatment for severe reactions) are designed for children weighing at least 33 pounds, or about 15 kilograms. Most 6-month-olds weigh far less than that. This doesn’t mean you shouldn’t introduce allergens. It does mean that introducing foods at home, during the day, with a phone nearby is a reasonable precaution. For babies at high risk of severe allergy, some pediatricians recommend doing the first introduction in a medical setting.
High-Risk Babies
Babies with severe eczema, an existing egg allergy, or a strong family history of food allergies are considered high risk. For these babies, early introduction is even more important, not less. The evidence is strongest for peanut: introducing it between 4 and 11 months is a proven prevention measure for high-risk infants. Your pediatrician may recommend allergy testing before the first introduction, particularly a skin-prick test for peanut, to determine whether a supervised introduction in a clinical setting is warranted.
For babies without these risk factors, home introduction with standard precautions is appropriate. Start small, watch closely for two hours, and keep the food in regular rotation once it’s tolerated.