A food allergy is an immune-mediated reaction — most commonly IgE-mediated — that can be life-threatening even with tiny exposures. A food intolerance is a non-immune reaction, usually dose-dependent, and rarely dangerous. Confusing the two leads to unnecessary restriction and sometimes to dangerous under-caution.
The key differences
| Feature | Food allergy | Food intolerance |
|---|---|---|
| Immune system involvement | Yes — IgE (immediate) or T-cell (delayed) | No (or non-IgE immune in some cases) |
| Dose required to react | Trace amounts can trigger | Usually dose-dependent |
| Onset of symptoms | Minutes to 2 hours (IgE); 6–48 hrs (non-IgE) | Hours to days |
| Severity | Can be life-threatening (anaphylaxis) | Uncomfortable but rarely dangerous |
| Symptoms | Hives, swelling, vomiting, anaphylaxis | Bloating, diarrhoea, headache, fatigue |
| Common examples | Peanut, tree nut, milk, egg, shellfish, wheat | Lactose, gluten (non-coeliac), fructose, histamine |
How food allergy is diagnosed
Diagnosis begins with a clinical history — symptom onset, timing relative to eating, severity and reproducibility. The most common diagnostic tests are skin prick tests (SPT) and specific IgE blood tests (previously called RAST or ImmunoCAP). A positive result means sensitisation — the immune system has produced IgE antibodies — but not necessarily clinical allergy. Many sensitised individuals tolerate the food in practice.
The gold-standard test for food allergy is an oral food challenge (OFC) — eating the food under controlled medical supervision. This is performed after initial testing when the results are ambiguous, or to assess whether a child has outgrown a diagnosed allergy.
Common food intolerances
Lactose intolerance — absence or reduction of the enzyme lactase — causes bloating, flatulence and diarrhoea after consuming dairy. It is confirmed by a hydrogen breath test or by lactase gene testing. Most people with lactose intolerance can tolerate small amounts (around 12 g of lactose — one glass of milk) without symptoms.
Non-coeliac gluten sensitivity (NCGS) is a diagnosis of exclusion: coeliac disease (autoimmune, confirmed by duodenal biopsy) and wheat allergy must both be ruled out first. A double-blind placebo-controlled food challenge is the only way to confirm NCGS, but is not routinely available.
The problem with self-diagnosis
Self-diagnosed food intolerances are common — studies suggest that while up to 20% of people believe they have a food allergy, clinical testing confirms it in only 2–4%. Unnecessary restriction of multiple foods can cause nutritional deficiencies, particularly in children, and significant lifestyle disruption without benefit.
Equally problematic: people who suspect only an intolerance when they have a genuine IgE-mediated allergy — and continue to consume small amounts of a food that could trigger anaphylaxis.
"Food symptom attribution is often wrong in both directions — too cautious where caution isn't needed, and too casual where it is."
Dr. Lina Haddad, CMO, Looms