Food Allergy vs Food Intolerance: How to Tell the Difference (UK Guide)

Why the difference matters

Many people use the terms "food allergy" and "food intolerance" interchangeably, but they describe two very different things. Confusing them can lead to unnecessary food avoidance, missed diagnoses, or — in the case of allergies — dangerous under-reaction to a genuine medical emergency.

According to the Food Standards Agency (FSA), around 2 million people in the UK live with a diagnosed food allergy. Food intolerance is believed to be more common, though exact numbers are harder to pin down because it's often self-diagnosed and not always reported to a GP.

Understanding the distinction helps you take the right steps: whether that's carrying an adrenaline auto-injector for a confirmed allergy, or keeping a food diary to identify intolerance triggers.

Food allergy vs food intolerance: at a glance

What is a food allergy?

A food allergy is an abnormal immune system response to a specific food protein. When someone with a food allergy eats (or sometimes even touches or inhales) the trigger food, their immune system produces immunoglobulin E (IgE) antibodies. These trigger the release of histamine and other chemicals, causing an allergic reaction.

Symptoms of a food allergy

Allergic reactions typically appear within minutes of exposure, though they can sometimes take up to two hours. Symptoms can range from mild to severe and may include:

• Skin: Itchy rash (hives/urticaria), swelling (angioedema), redness, eczema flare-ups
• Mouth and throat: Tingling or itching in the mouth, swelling of the lips, tongue, or throat
• Breathing: Wheezing, shortness of breath, nasal congestion, coughing
• Digestive: Nausea, vomiting, abdominal pain, diarrhoea
• Cardiovascular: Dizziness, fainting, rapid pulse, drop in blood pressure

How allergies are different from intolerances

The key distinction is the immune system's involvement. With an allergy, even a tiny trace of the food can trigger a reaction — sometimes a life-threatening one. You cannot simply "eat a little bit" of something you're allergic to. The amount does not reliably predict the severity of the reaction.

According to Allergy UK, food allergies affect around 6-8% of children and 2-4% of adults in the UK. Most childhood allergies to milk, egg, soya, and wheat are outgrown, but allergies to peanuts, tree nuts, fish, and shellfish tend to persist into adulthood.

The 14 major allergens in UK food law

Under UK food regulations — strengthened by Natasha's Law (October 2021) — food businesses must clearly declare the presence of 14 major allergens on all food labels, including food that is prepacked for direct sale (such as sandwiches made on the premises).

Natasha's Law was introduced following the death of Natasha Ednan-Laperouse in 2016 after eating a Pret a Manger baguette containing sesame, which was not labelled.

The 14 allergens that must be declared are:

1. Celery (including celeriac)
2. Cereals containing gluten (wheat, rye, barley, oats)
3. Crustaceans (prawns, crab, lobster)
4. Eggs
5. Fish
6. Lupin (a legume sometimes found in flour)
7. Milk (including lactose)
8. Molluscs (mussels, oysters, squid)
9. Mustard
10. Tree nuts (almonds, hazelnuts, walnuts, cashews, pecans, Brazil nuts, pistachios, macadamia nuts)
11. Peanuts
12. Sesame
13. Soya
14. Sulphur dioxide and sulphites (at concentrations above 10mg/kg or 10mg/litre)

These 14 allergens must be emphasised (usually in bold) in the ingredients list. If you have a confirmed food allergy, always check labels carefully. NutraSafe can help you scan food labels for allergens quickly.

What is a food intolerance?

A food intolerance is a difficulty digesting certain foods. Unlike an allergy, it does not involve the immune system and is not life-threatening. Intolerances are typically caused by:

• Enzyme deficiency — The most common example is lactose intolerance, where the body doesn't produce enough lactase to break down lactose (the sugar in milk).
• Sensitivity to food chemicals — Such as histamine (found in aged cheese, wine, cured meats) or caffeine.
• Sensitivity to food additives — Such as sulphites (used as preservatives in dried fruit and wine) or monosodium glutamate (MSG).
• Irritable bowel syndrome (IBS) — Certain foods (often high-FODMAP foods) can trigger IBS symptoms in susceptible people.

Symptoms of a food intolerance

Intolerance symptoms are primarily digestive and are not immediately dangerous, though they can significantly affect quality of life. They include:

• Bloating and abdominal distension
• Stomach cramps and pain
• Diarrhoea or loose stools
• Excessive wind (flatulence)
• Nausea
• Headaches (less common)
• Fatigue and general malaise (less common)

A crucial difference from allergies: intolerance symptoms are often dose-dependent. Someone who is lactose intolerant might tolerate a splash of milk in tea but experience symptoms after a large latte. With an allergy, the amount is largely irrelevant — even traces can cause a reaction.

Symptoms can also be delayed by hours, which makes identifying the trigger food more difficult. This is why keeping a detailed food and symptom diary is so important.

How to get tested

For food allergies (NHS pathway)

If you suspect a food allergy, your first step should always be your GP. Do not attempt to diagnose or test for allergies yourself.

Your GP may:

1. Take a detailed history — What you ate, when symptoms started, how long they lasted, and their severity.
2. Refer you to an NHS allergy clinic — For formal testing.
3. Arrange a skin prick test — Small drops of allergen solution are placed on your forearm and the skin is gently pricked. A raised bump (wheal) indicates sensitisation.
4. Order a specific IgE blood test — Measures the level of IgE antibodies to specific foods in your blood.
5. Supervise an oral food challenge — In a hospital setting, you eat gradually increasing amounts of the suspected food under medical supervision. This is considered the gold standard for allergy diagnosis.

For food intolerances

There is no single reliable medical test for food intolerance. The most effective approach is a supervised elimination diet:

1. Keep a food and symptom diary — Record everything you eat and any symptoms, including timing and severity. Use an app like NutraSafe to track your food reactions accurately.
2. Eliminate suspected foods — Under guidance from your GP or a registered dietitian, remove the suspected trigger food(s) for 2-6 weeks.
3. Monitor symptoms — If symptoms improve during the elimination phase, the food may be the trigger.
4. Reintroduce gradually — Add the food back in controlled amounts to confirm whether it causes symptoms to return.

Your GP may also test for specific conditions that mimic intolerance, such as coeliac disease (a blood test for anti-tTG antibodies) or inflammatory bowel disease.

Beware of unregulated "intolerance tests"

Food sensitivity: a third category?

You may have come across the term "food sensitivity" as a middle ground between allergy and intolerance. This isn't a formally defined medical term in the UK, but it's sometimes used to describe non-IgE-mediated immune responses to food — reactions that involve the immune system but don't produce IgE antibodies and don't cause anaphylaxis.

Examples include certain types of eczema triggered by food, and food protein-induced enterocolitis syndrome (FPIES) in infants. If you're unsure where your symptoms fit, your GP can help determine the right pathway. For a deeper look at the terminology, see our guide on food sensitivity vs intolerance vs allergy.

When to see your GP

Book an appointment with your GP if:

• You regularly experience symptoms after eating certain foods
• Symptoms are getting worse over time
• You have experienced any swelling of the lips, tongue, or throat after eating
• You have experienced any breathing difficulty after eating
• You are avoiding multiple foods and are concerned about nutritional deficiencies
• A child is showing signs of food allergy or intolerance
• You have a family history of allergies, eczema, asthma, or hay fever (atopy)

Living with food allergies or intolerances

Whether you're managing an allergy or an intolerance, keeping a clear record of what you eat and how your body responds is one of the most helpful things you can do. A food diary gives you — and your GP or dietitian — the evidence needed to identify patterns and make informed decisions.

For allergies, this means strict avoidance, label reading, and carrying medication. For intolerances, it often means understanding your personal threshold and making informed choices about what and how much to eat.

See our guide on common food intolerance symptoms for more on recognising the signs.

Frequently asked questions

What is the difference between a food allergy and a food intolerance?

A food allergy involves the immune system producing IgE antibodies in response to a specific food protein. It can cause severe, potentially life-threatening reactions including anaphylaxis, and symptoms usually appear within minutes. A food intolerance involves the digestive system and is typically caused by enzyme deficiency or sensitivity. Symptoms like bloating, cramps, and diarrhoea are uncomfortable but not dangerous, and can be delayed by several hours. If you suspect either, see your GP.

What are the 14 major allergens required on UK food labels?

Under UK food law (including Natasha's Law for prepacked for direct sale foods), the 14 major allergens that must be declared are: celery, cereals containing gluten (wheat, rye, barley, oats), crustaceans, eggs, fish, lupin, milk, molluscs, mustard, tree nuts, peanuts, sesame, soya, and sulphur dioxide (at concentrations above 10mg/kg or 10mg/litre). These must be emphasised — usually in bold — in the ingredients list.

Are IgG food intolerance tests reliable?

No. The NHS, NICE, and Allergy UK do not recommend IgG blood tests for diagnosing food intolerances. IgG antibodies to foods are a normal part of the immune response and simply indicate that you have been exposed to that food, not that you are intolerant to it. These tests are widely available commercially but have no scientific evidence supporting their use. If you suspect a food intolerance, speak to your GP about a supervised elimination diet.

How do I get tested for a food allergy in the UK?

See your GP, who can refer you to an NHS allergy clinic. Standard NHS allergy tests include a skin prick test (small amounts of allergen placed on the skin to check for a reaction) and a specific IgE blood test. In some cases, a supervised oral food challenge may be performed in a hospital setting. Do not attempt to test for allergies at home, as allergic reactions can be severe and unpredictable.

When should I see my GP about a food reaction?

See your GP if you regularly experience symptoms after eating certain foods, if symptoms are getting worse, or if you are avoiding multiple foods and worried about nutritional deficiencies. Call 999 immediately if you or someone else experiences signs of anaphylaxis: difficulty breathing, swelling of the throat or tongue, feeling faint or dizzy, or a rapid drop in blood pressure. Anaphylaxis is a medical emergency.

Related articles

• Common Food Intolerance Symptoms in the UK
• How to Track Food Intolerances with a Food Diary
• Food Sensitivity vs Intolerance vs Allergy: What's the Difference?
• Scan Food Labels for Allergens (UK)
• Food Reaction Tracker UK
• Food Intolerance Tracker UK

Last reviewed and updated: 7 February 2026