Few topics in infant and child health cause more confusion than food allergy versus food intolerance. The terms are used interchangeably in conversation, but they describe different processes with different management. Getting the distinction right helps you decide when avoidance is genuinely necessary, when it is overkill, and when "my child reacts to dairy" is being asked to do too much explanatory work.
Healthbooq covers children's health and infant feeding, including allergy and intolerance management.
True Food Allergy: Immune-Mediated
A food allergy is an immune reaction. In IgE-mediated allergy, the immune system flags a food protein as a threat and produces IgE antibodies. On subsequent exposure, the IgE antibodies trigger mast cells to release histamine and related mediators, producing the characteristic symptoms within minutes to 2 hours: urticaria (hives), angioedema (swelling), vomiting, abdominal pain, runny nose, wheeze, and in severe cases, anaphylaxis.
In non-IgE-mediated allergy, different immune mechanisms produce a delayed inflammatory response, typically over hours to days. This presents as eczema flaring after specific foods, persistent vomiting, blood-streaked stool in babies, or chronic loose stools. Cow's milk protein allergy in infants is often non-IgE-mediated.
Both forms are immune-mediated — the immune system is generating a response to the food protein.
Food Intolerance: Non-Immune-Mediated
Food intolerance does not involve the immune system. Symptoms are dose-dependent (a teaspoon of yoghurt may be fine; a glass of milk causes problems), almost always digestive, and never life-threatening. The typical pattern is bloating, wind, abdominal cramps, and loose stools an hour or two after eating.
Lactose intolerance is the most common form. It results from low levels of lactase, the enzyme in the small intestinal lining that digests lactose (the sugar in milk).
- Primary lactase deficiency is genetic and lifelong. It is unusual in young children — most children, especially those of European ancestry, maintain high lactase production through childhood. It typically emerges from late primary school onward and is the norm in the majority of the world's adult population outside Northern Europe.
- Secondary lactase deficiency is common in young children. Viral gastroenteritis (rotavirus historically; now more often norovirus) damages the lactase-producing cells lining the small intestine. A child who develops bloating and loose stools whenever they have dairy after a stomach bug usually has secondary lactose intolerance, which resolves in 4-6 weeks as the gut heals. They do not need to avoid dairy long-term.
Non-coeliac gluten sensitivity is a proposed condition that is not well-established in young children. Be cautious about removing gluten from a child's diet without coeliac disease being ruled out first — coeliac antibody tests only work if gluten is in the diet at the time of testing.
Why the Distinction Matters
True food allergy needs strict avoidance, antihistamines for mild reactions, and an adrenaline auto-injector if there is anaphylaxis risk. Accidental exposure can be serious. The child needs an allergy action plan and ongoing review.
Food intolerance generally allows dose-dependent management. A child with lactose intolerance may handle small amounts of dairy, hard cheese (most lactose has been broken down in maturation), and live yoghurt (bacteria help digest the lactose) without symptoms. They do not need an auto-injector and they do not need their school informed of an allergy.
Over-diagnosis is a real problem. UK paediatric allergy services regularly see families on highly restrictive diets based on self-diagnosis or unvalidated tests (IgG testing, hair analysis, kinesiology — none of these diagnose food allergy or intolerance, despite their commercial availability). Eliminating dairy from a young child's diet risks calcium and vitamin D deficiency. Multi-food exclusion in a toddler can produce iron, iodine, and energy shortfalls. Restriction should follow a confirmed diagnosis, not a hunch.
When to Seek Allergy Testing
Testing is appropriate when symptoms suggest IgE-mediated allergy (rapid reaction within 2 hours of a specific food), when the family is considering significant dietary exclusion, or when symptoms have been blamed on multiple foods without a clear pattern. Skin prick testing and specific IgE blood tests can confirm IgE-mediated sensitisation, with specialist interpretation — a positive test alongside a clear history confirms allergy; a positive test without symptoms (sensitisation only) does not. Neither test is reliable for non-IgE-mediated reactions, which are diagnosed by carefully supervised elimination and reintroduction.
For suspected secondary lactose intolerance after gastroenteritis, no test is needed — try low-lactose dairy or a brief dairy break for 2-4 weeks, then reintroduce, and watch what happens.
Key Takeaways
Food allergy and food intolerance are different conditions that often get muddled together. True food allergy is an immune reaction to a food protein and can range from mild hives to anaphylaxis. Food intolerance is non-immune-mediated, dose-dependent, and produces digestive symptoms — there is no anaphylaxis risk. The most common food intolerance in children is secondary lactose intolerance after gastroenteritis, which usually resolves in 4-6 weeks as the gut heals. Primary lactose intolerance (genetic, lifelong) is rare in children and typically appears from late primary school onward. Over-restrictive diets based on suspected intolerance are a real problem — eliminating dairy in young children risks calcium and vitamin D deficiency, so confirmation matters before exclusion.
