Short answer: A food allergy is a reaction of the immune system. It usually starts within minutes to two hours of eating (for cows' milk allergy, sometimes up to a few days), and it can occasionally be severe. A food intolerance is a difficulty digesting a food; it mainly causes gut symptoms a few hours later and isn't life-threatening. Don't cut major foods out of your child's diet without advice: talk to your GP, who can arrange proper testing and, if needed, a dietitian. Call your emergency number for swelling of the lips, tongue or throat, or difficulty breathing.
A rash after yoghurt. Tummy ache after milk. And the internet says: just cut it all out and see. Please don't do that without advice — that's the heart of this article.
The difference
Food allergy
The immune system reacts to a food as if it were harmful. In babies and young children, reactions usually happen quickly — within a few minutes of trying a food, though it can take up to two hours. With some allergies, such as cows' milk allergy, symptoms can take up to three days to appear.
Possible symptoms include:
- swollen lips or face; red, itchy, watery eyes;
- a red, itchy rash or hives, or worsening eczema;
- wheezing, coughing, sneezing or a runny nose;
- being sick, tummy pain, diarrhoea or constipation.
Most allergic reactions are mild. Occasionally a severe reaction (anaphylaxis) happens, with breathing problems, a swollen throat or tongue, or a child becoming floppy or unresponsive. That's an emergency.
Food intolerance
An intolerance isn't an immune reaction but a difficulty digesting something — the most common is lactose intolerance. Symptoms usually come a few hours after eating and are mainly bloating, wind, diarrhoea and tummy pain. It's unpleasant, but not dangerous, and the amount eaten often matters.
With an allergy, even a small amount can trigger a reaction. With an intolerance, it's usually about how much.
Why not to cut foods out yourself
- Nutrition: cutting out a major food such as milk without a proper replacement can mean your child misses out on nutrients like calcium and protein.
- Diagnosis: it becomes harder to work out what's really going on.
- Allergy risk: for babies, the NHS advises that allergenic foods, once introduced and tolerated, should stay a regular part of the diet to minimise the risk of allergy.
What to do instead
- Keep a food and symptom diary: what your child ate, when, what happened, how soon afterwards and for how long.
- Take it to your GP. They may refer your child to a specialist.
- Testing may include a skin-prick test or blood tests, and sometimes a carefully supervised food challenge in hospital.
- If an allergy is confirmed, a registered dietitian can help keep your child's diet complete.
Beware of unreliable tests. UK clinical guidance (NICE) advises against using serum IgG tests, vega testing, applied kinesiology or hair analysis to diagnose food allergy. These are often sold online and can lead to unnecessary restrictions.
Cows' milk allergy in babies
Cows' milk allergy is one of the most common food allergies in babies, and many children outgrow it. If your baby isn't breastfed, they may need a special formula prescribed by a doctor. If you're breastfeeding, you may be advised to cut out dairy yourself — but only with medical advice, and with support to keep your own diet balanced. Goats' milk formula isn't suitable for babies with cows' milk allergy.
Introducing allergenic foods
For most babies, foods such as egg, peanut and wheat can be introduced from around six months, one at a time. If your baby already has eczema or a food allergy, or there's a family history of allergies, talk to your GP or health visitor first. See starting solids.
In an emergency
Call 999 (UK), 911 (US) or 112 (EU) if your child has swelling of the lips, mouth, tongue or throat, is struggling to breathe or wheezing, has blue, grey or pale skin or lips, or becomes floppy, drowsy or unresponsive. If your child has been prescribed an adrenaline auto-injector, use it straight away, then call for an ambulance. Lie your child down (or sit them up if they're struggling to breathe) and don't let them stand or walk.
If your child has a diagnosed allergy, make sure nursery, school and anyone who looks after them knows what to avoid and what to do — ideally with a written allergy action plan.
Related reading
Introducing foods with confidence: First Bites (PDF, English) covers weaning from the first spoon to self-feeding, for babies and toddlers up to 24 months.
Sources
- NHS — Food allergies in babies and young children.
- NHS — Food allergy and Food intolerance.
- NHS — Anaphylaxis.
- NICE — Food allergy in under 19s: assessment and diagnosis (CG116).
- American Academy of Pediatrics, HealthyChildren.org — Food allergies in children.
Written by the Bloom Guides editorial team. Last updated: 20 October 2026. General information only — not a substitute for advice from your GP, allergy specialist or dietitian.