Allergy and intolerance are often used interchangeably, but they are different conditions with different mechanisms, different presentations, and different management. Understanding the distinction matters practically — because the management of a true food allergy (particularly one with anaphylaxis risk) is fundamentally different from managing an intolerance. For a comprehensive overview, see our complete guide to child health.
The Fundamental Difference
Food allergy involves an immune system response to a specific food protein. The immune system mistakenly identifies the food as harmful and mounts a response — either via IgE antibodies (causing immediate symptoms) or via other immune mechanisms (causing delayed symptoms). Even small amounts of the food can trigger a reaction.
Food intolerance does not involve the immune system. The body has difficulty processing or digesting a particular food component. Reactions tend to be dose-dependent — small amounts may be tolerated; larger amounts cause symptoms. Symptoms are usually gastrointestinal (bloating, diarrhoea, pain) and resolve when the food is avoided. There is no risk of anaphylaxis.
Common Food Allergies in Babies
- Cow's milk protein allergy (CMPA): The most common food allergy in infants. Immune-mediated. Can cause immediate reactions (hives, vomiting shortly after feeding) or delayed reactions (eczema, blood in stools, persistent reflux). Not the same as lactose intolerance.
- Egg allergy: Common in infants and young children. Most outgrow it.
- Peanut and tree nut allergy: Can be severe and persistent.
- Wheat allergy: Distinct from coeliac disease (also immune-mediated but different mechanism).
- Soy allergy: Occurs in some babies with CMPA, as soy protein shares similar structure.
Lactose Intolerance vs Cow's Milk Protein Allergy
This is one of the most common points of confusion. They are different conditions:
Lactose intolerance:- Non-immune mechanism
- Inability to digest lactose (the sugar in milk) due to insufficient lactase enzyme
- Symptoms: bloating, gas, diarrhoea — usually dose-dependent
- Primary lactose intolerance (genetic, permanent) is extremely rare in infants — it would manifest immediately and severely from birth
- Secondary lactose intolerance can occur temporarily after a gut infection that damages the small intestine lining; it resolves as the gut heals
- Not the same as CMPA; lactose-free formula does not treat CMPA
- Immune-mediated response to the proteins in cow's milk (casein and whey)
- Can cause a wider range of symptoms including skin, gut, and respiratory symptoms
- Requires strict avoidance of cow's milk protein (not just lactose)
- Treated with extensively hydrolysed or amino acid-based formula (not lactose-free formula)
Gluten Intolerance vs Coeliac Disease
Similarly, there is frequent confusion between:
Non-coeliac gluten sensitivity (NCGS): A non-immune reaction to gluten causing gastrointestinal symptoms. Poorly understood. Does not cause the intestinal damage seen in coeliac disease.
Coeliac disease: An immune-mediated reaction to gluten that causes small intestinal damage, nutrient malabsorption, and a range of symptoms. Requires strict lifelong gluten avoidance. Diagnosed via blood tests (TTG antibodies) and often confirmed by intestinal biopsy.
Coeliac disease in infants and toddlers presents with: faltering growth, diarrhoea, abdominal distension, irritability, and reduced appetite, typically after gluten is introduced (from 6 months).
How to Tell Them Apart in Practice
Both allergy and intolerance may present with overlapping gut symptoms. Clues that point toward allergy rather than intolerance:
- Immediate timing after exposure (within minutes to 2 hours)
- Skin symptoms (hives, eczema flares)
- Respiratory symptoms
- Failure to thrive
- Severe reactions that don't seem dose-dependent
- Family history of allergy
When in doubt, discuss with your GP. Testing for food allergy (skin prick tests, specific IgE blood tests) can provide clarity. There is no reliable blood test for most food intolerances; diagnosis is usually clinical and based on elimination and reintroduction.
Key Takeaways
Food allergy involves immune system response and can cause immediate reactions (hives, swelling) or delayed reactions (eczema, failure to thrive); even small amounts trigger reactions and anaphylaxis is possible. Food intolerance is non-immune, dose-dependent, causes primarily gastrointestinal symptoms, and carries no anaphylaxis risk. Lactose intolerance is an intolerance; cow's milk protein allergy is a true immune-mediated allergy requiring strict protein avoidance. Coeliac disease is immune-mediated gluten sensitivity causing intestinal damage; non-coeliac gluten sensitivity is non-immune and poorly understood.
