The information within this post is for general advice only. If your child is experiencing symptoms of an allergic reaction, speak to your health care professional

Key highlights:

• Cow’s milk, egg, nuts, soy, wheat, sesame, fish and shellfish are some of the most common baby allergens.
• Some signs of a food allergy in a baby include skin reactions like hives or rashes; digestive issues such as vomiting or diarrhoea; respiratory symptoms like coughing or wheezing; and behavioural changes such as increased fussiness or lethargy.
• Babies will typically show signs of an allergic reaction within minutes to two hours after eating.
• Introduce allergen foods one at a time in small amounts.

Introducing your baby to new foods is an important step in their food journey. But it can also feel overwhelming, even a little scary - especially when it comes to introducing allergens. You’re not alone. Many parents are unsure about how to offer these foods safely.

Introducing common allergen foods early and regularly may help reduce the risk of developing food allergies, particularly for babies who have eczema or a family history of allergies.¹

In this article, we’ll take a closer look at some common allergen foods for a baby, what to look for when introducing them and how to introduce them into your child’s diet. With the right information, allergen introduction can become a calm and positive part of your baby's feeding routine.

What are the most common food allergies in babies?

Some foods are more likely than others to trigger allergic reactions in babies. While most tolerate these without issue, it's important to be aware of higher-risk foods. Here are some common allergen-containing foods to keep in mind.²

• Cow’s milk (dairy)
• Egg
• Nuts including peanut and tree nuts
• Soy
• Wheat
• Sesame
• Fish
• Shellfish

While these are some of the more common food allergens , your little one may also have reactions of allergy to less common foods and ingredients. That’s why it's important to introduce new foods one at a time and then observe closely for any symptoms.

Signs of food allergies in babies

Food allergy symptoms can show up in different ways. Some are mild and appear within minutes, while others may take a little while longer and are more difficult to recognise. Some common symptoms of a food allergy in a baby include:³

Skin symptoms:

• Redness or rash around the mouth or face
• Hives
• Swelling of the lips, eyes or face

Digestive symptoms:

• Vomiting
• Diarrhoea
• Abdominal pain

Respiratory symptoms:

• Coughing
• Noisy breathing
• Wheezing
• Sneezing or runny nose

Behavioural signs:

• Sudden fussiness or irritability
• Refusal to eat

Baby food allergy symptoms and presentation can vary. Speak to your healthcare professional to understand more about managing symptoms.

What does baby allergy poo look like?

Parents often find themselves examining their baby’s nappy a little more closely when suspecting a food allergy. Changes in a baby’s stool (poo), such as colour variation, mucus, or unusually loose and watery consistency, can be signs of a food sensitivity or allergy, but they aren’t always conclusive on their own.

In babies with cow’s milk protein allergy, stools may be more runny than usual and can occasionally contain mucus. These symptoms can indicate possible gut irritation.⁵ However, it can also line up with other digestive infections or minor irritation, so it's always best to speak to your child’s healthcare provider for a clear diagnosis.

While these signs may be concerning, they’re not always caused by food allergies., temporary tummy upsets, or changes in diet can also cause similar symptoms. If something feels off, trust your instincts and reach out to your baby’s doctor.

How long after eating will a baby show an allergic reaction?

Most babies with a food allergy will show symptoms soon after eating but a mild to moderate reaction may take up to 24 hours.⁹

In some cases, allergic reactions may not appear straight away. Some babies may show signs a few hours after eating, usually around four to six hours later. These delayed signs often affect the tummy and include symptoms like vomiting and diarrhoea. They can often be hard to link to a specific food because of the time gap.¹⁰

Whether symptoms appear quickly or after a delay, it’s a good idea to keep a food diary and introduce new foods one at a time to make it easier to pinpoint any triggers.

How to introduce allergen foods for a baby

Introducing high allergy foods to a baby is an important milestone in your baby’s development. While it might feel a little daunting at first, having a clear approach can help you feel more confident.

Current guidance from the Australiasian Society of Clinical Immunology and Allergy (ASCIA) recommends starting to introduce allergens around six months of age, or when a child is showing signs of readiness, but not before four months. You should always introduce one new food at a time, in very small amounts, alongside other solids that your baby is already tolerating well.¹

Here are a few tips to keep in mind:¹

• Choose a time when your baby is well. Avoid introducing new foods when they’re unwell or unsettled.
• Start small. A fraction of teaspoon of food is all you need. For example, a quarter teaspoon of well-cooked egg or smooth peanut butter rubbed onto your baby’s lip. Gradually increase the amount offered with each new mealtime.
• One at a time. This makes it easier to identify what food has caused the reaction.
• Watch for signs. Most reactions appear shortly after exposure, so keep a close eye on your baby.
• Offer new foods earlier in the day. This helps you monitor your child’s behaviour more closely, rather than just before bed.
• Keep it regular. If tolerated, ongoing exposure is important to help maintain tolerance.
• Follow all other good infant feeding principles. Ensure food is safely stored, prepared, well-cooked in the case of perishable foods like meat and eggs, and an appropriate texture for your baby’s developmental stage.

You don't need to rush through the list of allergenic foods. Instead, work at a pace that is comfortable and always check in with your GP if you have specific concerns.

Supporting your baby through their allergen journey

Food allergies can feel overwhelming at first, but with the right information they’re usually manageable. Understanding the signs, how to introduce allergen foods and knowing when to seek help are all part of navigating this stage with confidence. What’s most important is observing your baby, staying curious about how they respond to new foods, and working closely with your GP, an Accredited Practising Dietitian or child health nurse if you ever feel unsure.

Looking for more information on baby allergens and guides? Head over to the Biostime Parent Lounge for more articles and useful tips.

References

1. Australasian Society of Clinical Immunology and Allergy. Infant feeding and allergy prevention guidelines. Available from: https://www.allergy.org.au/hp/papers/infant-feeding-and-allergy-prevention
2. Australasian Society of Clinical Immunology and Allergy. Common food allergy triggers: egg, cow’s milk, peanut, tree nuts, sesame, soy, wheat, fish and shellfish. ASCIA Fast Facts – Food Allergy. Available from: https://www.allergy.org.au/patients/fast-facts/food-allergy
3. Australasian Society of Clinical Immunology and Allergy. Updated anaphylaxis guidelines: management in infants and children. Australian Prescriber. 2021;44(3):—. Available from: https://australianprescriber.tg.org.au/articles/updated-anaphylaxis-guidelines-management-in-infants-and-children.html
4. Kids With Food Allergies / Asthma and Allergy Foundation of America. Food Allergy Anaphylaxis in Infants and Toddlers. Available from: https://kidswithfoodallergies.org/research/our-food-allergy-research/food-allergy-anaphylaxis-in-infants
5. Medical News Today. Milk allergy and baby poop: Pictures, symptoms, and treatment. Available from: https://www.medicalnewstoday.com/articles/milk-allergy-baby-poop-pictures
6. IABLE. Infant Allergic Proctocolitis and Bloody Stools. Available from: https://lacted.org/iable-breastfeeding-education-handouts/proctocolitis/
7. Medical News Today. Milk allergy and baby poop: Pictures, symptoms, and treatment. Available from: https://www.medicalnewstoday.com/articles/milk-allergy-baby-poop-pictures
8. Vandenplas Y, et al. [Management of functional gastrointestinal disorders and cow’s milk protein allergy in infants]. Acta Paediatr. (online guidelines). Available from: https://onlinelibrary.wiley.com/doi/epdf/10.1111/apa.13311
9. Australasian Society of Clinical Immunology and Allergy. Food Allergy – Clinical Update for Health Professionals. Available from: https://www.allergy.org.au/hp/papers/food-allergy-clinical-update
10. Clinical Practice Guidelines: Non‑IgE mediated food allergy. Available from: https://www.rch.org.au/clinicalguide/guideline_index/Non-IgE_mediated_food_allergy/