How to Diagnose a Food Allergy or Intolerance in Babies and Toddlers
All your questions answered about diagnosing a food allergy or intolerance. Written by Registered Baby and Child Dietitian, and Milk Allergy Specialist, Christina Hills.
When your baby seems uncomfortable after feeding- maybe they are more unsettled that unusual, gut issues like constipation or loose poop, eczema that won’t go away - it’s natural to wonder whether food might be to blame.
But food reactions can be complex - so getting a clear diagnosis helps you understand what’s really going on and ensures your baby gets the right support.
Step 1: A Detailed History
The first and most important step is a really good conversation about your baby’s story so far. We will explore your baby’s feeding patterns, symptoms, timing, and family allergy history- helping to piece together the bigger picture of what might be going on.
We will look for patterns- for example, do symptoms appear immediately after feeding, or hours later? Are they always linked to one food?
Step 2: Allergy Testing (When Appropriate)
If an IgE-mediated allergy is suspected (the type that causes quick reactions like hives, swelling, vomiting or breathing changes), the following tests n ay be recommended:
Skin prick testing, or
Specific IgE blood tests (sometimes called RAST tests)
These tests look for antibodies in the blood that react to specific foods.
If a non-IgE allergy (delayed reaction) is suspected, testing usually isn’t helpful-instead, diagnosis relies on the next step.
Step 3: Elimination and Reintroduction
For delayed reactions, a dietitian will support with a short elimination diet, removing the suspected foods (like milk, egg or soy)
For delayed reactions, your paediatric dietitian will guide you through an elimination and reintroduction process- removing the suspected foods (such as milk, egg or soy) usually for 2–4 weeks, but sometimes longer, and then carefully reintroducing them to see whether any symptoms return. The process may need to be repeated several times to get a clear picture. This approach should always be carried out with professional support to ensure your baby’s diet stays nourishing and safe, and that each step is done at the right time and pace for your little one.
Diagnosis can feel like a journey- but getting clarity is the first step toward calmer feeding and happy tummies.
Need Extra Support?
If you’d like one-to-one guidance through an allergy diagnosis, reintroduction, or allergy-safe weaning, I offer personalised consultations to help you feel informed, and supported through every stage of your child’s allergy journey.
👉 Book a session or explore more resources in the Milk Allergy Hub.