Allergy or intolerance? Understanding the difference
Updated: Oct 3
When a food seems to upset your child, it is natural to reach for the word "allergy". But not every reaction to food is an allergy. Some are intolerances, and the two are quite different. Knowing which you are dealing with changes how you manage it, so it is worth understanding.
What is a food allergy?
A food allergy involves the immune system. The body mistakes a harmless food for a threat and reacts. Allergic reactions tend to be:
Quicker, often within minutes to a couple of hours
Triggered by even small amounts of the food
Linked to symptoms like hives, swelling, vomiting, and in serious cases breathing difficulty
Because allergies can occasionally be severe, they are the type that need the most care.
Not every food allergy is quick, though. Some, called delayed or Non-IgE Food Allergy, can take several hours or even days to show. These reactions often affect the skin or tummy, for example Eczema flares, Reflux, tummy pain or changes in stools. Cow's Milk Protein Allergy in babies is a common example. Because the signs are slower and can look like an intolerance, this type can be harder to spot, which is why taking time to go through your child's full history really helps.
What is a food intolerance?
An intolerance does not involve the immune system. It usually means the body struggles to digest something, like the lactose in milk.
Intolerances tend to be:
Slower, building up over hours
Dose related, so a small amount may be fine but a lot causes trouble
More about the tummy, such as bloating, wind, cramps and loose stools
Intolerances can be uncomfortable and miserable, but they are not life threatening in the way a severe allergy can be.
A quick side-by-side
Speed: Immediate allergy is fast, delayed (Non-IgE) allergy can take hours or days, and intolerance is usually slower
Amount: Allergy can react to a tiny amount, intolerance is usually about quantity
Symptoms: Allergy often involves skin and swelling, intolerance is mostly digestive
Risk: Allergy can sometimes be serious, intolerance is uncomfortable but not dangerous
Why the difference matters
Getting this right matters because it shapes everything that follows. An allergy may mean strictly avoiding a food and having a plan for reactions. An intolerance may mean simply limiting a food rather than cutting it out completely. Cutting whole food groups from a child's diet without good reason can affect their nutrition, so it is not something to do on a hunch.
How to find out
Keeping a simple food and symptom diary is a great first step. Note what was eaten, when, and what happened. That pattern often gives a strong clue, and it is really useful information to bring to a professional.
Getting clarity
If you are not sure whether your child has an allergy or an intolerance, you do not have to guess. A nurse-led consultation can help you make sense of the pattern, decide on sensible next steps, and work alongside your GP, who can arrange testing or referral if needed.
What we do and do not provide
Allergy Nurture Nurses is a CQC-registered, nurse-led allergy and allergy-triggered Asthma advisory service for children, young people and families.
We provide assessment through taking an allergy-focused history, education, support and practical guidance. We do not provide emergency medical care, allergy testing, medical diagnosis or prescribing. Where appropriate we can liaise with the patient's GP and signpost to appropriate services. Where further medical assessment is required, families will be advised to contact their GP, NHS services or an appropriate healthcare professional. In a medical emergency, call 999.
Your baby or child should remain under their GP, NHS team or relevant healthcare professionals for clinical diagnosis, medical treatment, prescribing and urgent care.
When should I seek urgent medical help?
Most allergy symptoms are not emergencies. However, allergic reactions can occasionally become serious very quickly.
Call 999 immediately if your baby or child develops difficulty breathing, significant swelling of the tongue or throat, becomes floppy, collapses, appears severely unwell or develops symptoms of Anaphylaxis.
Urgent medical advice should also be sought if your child is becoming unwell. Urgent symptoms are not suitable for a routine consultation or online enquiry.
This blog is general guidance and not a substitute for medical advice. Allergy testing and diagnosis should be done through your GP or specialist. Please do not remove major foods from your child's diet without advice, and call 999 in an emergency.
About the author
Written and clinically reviewed by Catherine Neale, NMC Registered Children's Nurse and Clinical Nurse Specialist, and founder of Allergy Nurture Nurses. Catherine has over 25 years' nursing experience, including 7 years as a specialist allergy nurse, and is a member of the British Society for Allergy and Clinical Immunology (BSACI).
Last clinically reviewed: 28 September 2026.
