Allergy, intolerance and coeliac are different problems.

Three different mechanisms

A food allergy is the immune system overreacting to a food. An intolerance is difficulty digesting a food or ingredient — no immune involvement. Coeliac disease is autoimmune: the immune system attacks the body's own gut tissue when gluten is eaten. Source: NHS food intolerance (opens in a new tab) Source: NHS coeliac disease (opens in a new tab).

The consequences differ too. An allergy can mean strict avoidance and an emergency plan; an intolerance usually means finding the amount you personally tolerate; coeliac disease means a medically supervised, lifelong gluten-free diet. Same family of complaints — three very different rulebooks.

Three mechanisms, three different conversations — with your GP, and with anyone cooking for you. Keeping them straight matters most at the two moments it counts: describing symptoms to a clinician, and describing needs to a kitchen.

Allergy: the immune-system reaction

A food allergy is the immune system treating a food as a threat. Symptoms can affect different parts of the body at once — itchy skin or a raised rash, swelling of the lips, face and eyes, coughing or wheezing, stomach pain — and can start soon after eating, or days later. Source: NHS food allergy (opens in a new tab).

Most reactions are mild, but some are serious. Sudden swelling of the mouth, tongue or throat, struggling to breathe or swallow, or someone becoming limp or unresponsive can be signs of anaphylaxis — call 999 immediately, and use a prescribed adrenaline auto-injector or nasal spray first if one is available. Source: NHS food allergy (opens in a new tab).

The NHS names the most common culprits — cows' milk, eggs, peanuts, tree nuts, shellfish, wheat and some legumes like soy and peas — while noting that any food can cause an allergy. Your chance is a little higher if close family have allergies, asthma or eczema. Source: NHS food allergy (opens in a new tab).

Suspect one? The NHS route is a GP, who can refer you to a specialist for tests — a skin-prick test, blood tests, or a supervised diet where you avoid the suspect food to see if symptoms settle. That structured exclusion is what separates a confirmed allergy from a hunch. Source: NHS food allergy (opens in a new tab).

Intolerance: digestion, not immunity

A food intolerance is difficulty digesting a food or ingredient — lactose, the sugar in milk, is the most common example. Symptoms tend to be gut-led (bloating, tummy pain, diarrhoea, wind) and usually arrive a few hours after eating. Miserable, sometimes long-lasting — but not immune-driven, so an intolerance cannot cause anaphylaxis. Source: NHS food intolerance (opens in a new tab) Source: Allergy UK on allergy vs intolerance (opens in a new tab).

One caution on diagnosis: the NHS warns that shop-bought intolerance tests have limited evidence and can wrongly suggest cutting out many foods. Do not remove foods from your diet — or your child's — on a test's say-so without a GP or dietitian involved. Source: NHS food intolerance (opens in a new tab).

Almost any food or ingredient can be the trigger: alongside lactose, the NHS names gluten-bearing grains, histamine in wine and aged cheese, caffeine, alcohol and sulphites. Because symptoms often scale with how much you ate, many people find a tolerable threshold rather than a permanent ban — which is why the diary habit described below earns its keep. Source: NHS food intolerance (opens in a new tab).

Coeliac disease: autoimmune, not an allergy

Coeliac disease is neither an allergy nor an intolerance: the immune system attacks the body's own tissues when gluten — a protein in wheat, barley and rye — is eaten, damaging the small intestine's surface and its ability to take in nutrients. Source: NHS coeliac disease (opens in a new tab).

It is common — estimated at least 1 in 100 people in the UK, with milder cases likely underdiagnosed — and the treatment is a strict gluten-free diet, for life. Testing usually starts with a blood test via a GP; the NHS advises keeping gluten in your diet until testing is finished, because avoiding it can make results inaccurate. Source: NHS coeliac disease (opens in a new tab).

Gluten is not a fringe ingredient — it runs through pasta, most breads, breakfast cereals, cakes and more sauces and ready meals than you'd guess. And because the condition is partly hereditary, the NHS recommends testing for first-degree relatives of people diagnosed with it — worth remembering if it runs in the family. Source: NHS coeliac disease (opens in a new tab).

Why the label you use matters at a restaurant

'Allergy' and 'intolerance' sound interchangeable in conversation but lead a kitchen differently. A declared allergy — or coeliac disease — asks for the formal allergen information and cross-contact care; an intolerance asks what is in the dish so you can judge how much, if any, is comfortable for you.

The legal vocabulary helps here: UK businesses must tell you about the 14 mandated allergens, and wheat starch or shared fryers matter differently to someone with coeliac disease than to someone who simply avoids gluten. If you have coeliac disease, say so explicitly.

In practice that means saying the precise word plus the specific food: "I'm allergic to sesame" or "I have coeliac disease" gives the kitchen a different job than "I'm a bit intolerant of onion". Vague words get vague handling; the right word gets the right process.

For the actual conversation — what to ask, when to call ahead — the eating-out checklist turns these definitions into questions.

Getting diagnosed properly

Only a clinician can tell these apart for certain. The practical route: keep a short food-and-symptoms diary — what you ate, when, what happened and how quickly it came on — take it to your GP, and let testing do the sorting: skin-prick or blood tests for allergy, supervised elimination diets for intolerance, a blood test and possibly a biopsy for coeliac disease. Source: Allergy UK on allergy vs intolerance (opens in a new tab) Source: NHS food allergy (opens in a new tab).

For suspected intolerance specifically, a GP may refer you to a dietitian, and the NHS describes tests that can include a special diet — avoiding the food for a few weeks, then reintroducing it to see whether symptoms return — plus blood tests and a breath test where lactose is the suspect. Source: NHS food intolerance (opens in a new tab).

Two honest limits. This page is orientation, not a symptom checker — it cannot weigh your symptoms. And a Food Says Hi lookup can describe a dish's likely identity and context; it cannot diagnose a reaction or declare a food safe for you. If something you eat keeps making you ill, that is a GP conversation.