Food allergy vs intolerance: Your simple guide to best management

Food allergies involve the immune system and can trigger sudden life-threatening reactions. Food intolerances are non-immunologic. They cause digestive and other symptoms that appear gradually and can be debilitating but are usually lower risk.¹ Understanding the difference and getting the right diagnosis will help you manage your condition safely.

Over 30% of adults in a community survey for the Food Standards Agency said they have adverse reactions to food (Patterns and Prevalence of Adult Food Allergy (PAFA), 2024). According to the same report, only around 6% of UK adults have a confirmed food allergy. It’s likely intolerance-type symptoms, which are harder to diagnose, may partly explain this disparity.²

It is common to confuse allergy and intolerance because some symptoms are common to both conditions and triggers can overlap.¹ This article explains what those symptoms are and also how to recognise the different types of food allergies and intolerances. Read more detailed definitions of both conditions. We also cover what tests are available to help doctors make their diagnosis, as well as  treatments and strategies to help you stay well. At the end, you’ll find answers to some frequently asked questions about food allergies vs intolerance.

What is food intolerance definition?

Food intolerance defines a range of poorly understood disorders linked by not being an immune response. Intolerance can stem either from personal factors, like enzyme deficiency, or from properties of the food. Symptoms often affect more than one part of the body – the severity depends on the amount of food eaten.¹

People with food intolerance may be able to tolerate a certain amount of the offending food before they get symptoms, according to the review, Food Intolerances, published in the journal Nutrients (2019). This varies from person to person.⁴

Host-dependent food intolerance

Lactose and fructose both cause what’s called host-dependent food intolerance, meaning there’s a personal factor. People who don’t make enough of the enzyme lactase may feel bloated and get diarrhoea when they eat dairy products.¹ Lack of aldolase B, another enzyme, makes it hard to digest fructose.³ Fructose intolerance can also refer to fructose malabsorption, when cells in your intestine can’t absorb the fruit sugar in fruit and honey.³

Fructose and lactose are fermentable carbohydrates (FODMAPs). Others linked to food reactions include: polyols, found in avocado and pear; fructans, in wheat, onion and garlic; and galacto-oligosaccharides, in legumes and nuts. Intolerance symptoms may result from visceral hypersensitivity.⁴ This makes the ordinary process of food passing through the digestive system painful.⁵

Gluten intolerance, or non-coeliac gluten sensitivity, is host-dependent too. Scientific studies often can’t reproduce the symptoms so the mechanism is still unclear, according to Food Allergy and Intolerance: A Narrative Review on Nutritional Concerns (Nutrients, 2021).¹

Host-independent food intolerance

This type of food intolerance can be due to naturally occurring chemicals like histamine or to food additives. Sulphites and benzoates, used as preservatives, are intolerance triggers. So is the flavour-enhancer monosodium glutamate. If you get symptoms from seemingly unrelated foods, it could be that a chemical is the link.¹

Other natural food chemicals that may cause food intolerance symptoms include caffeine and salicylates, found at high levels in some fruit, vegetables, herbs, spices and nuts.^1,6 There’s histamine in fresh food too, but also wine, chocolate, fermented food like miso and kimchi, aged cheese, cured meat, and both fresh and preserved fish and seafood.⁷

Is there a test for food intolerance?

Testing for food intolerance is not as advanced as it is for allergies and there’s no reliable test except for lactose intolerance, according to the British Society for Allergy and Clinical Immunology.^xx For this, your GP may suggest a hydrogen breath test. Or they may check your blood sugar levels after asking you to drink a lactose solution or milk.¹¹

Other tests offered for food intolerance are medically unproven. That includes IgG and IgG4 blood tests. These types of tests may show you have an antibody response to certain foods. But studies suggest this might simply be because it’s a food you eat regularly. Positive hair strand analysis and kinesiology may lead people to stop eating whole food groups when they don’t need to.¹⁰

The gold standard for diagnosing food intolerance is a supervised elimination diet.¹⁰

So how do I find out if I have a food intolerance?

Your GP will take your medical history, including details of any allergies. Keep a food and symptoms diary to show them, checking ingredients lists on pre-packaged foods to see if there’s a common factor.¹ The doctor may then suggest removing a particular food from your diet for a certain period.

A typical elimination diet and follow-up might go like this:¹

• Cutting out foods that cause food intolerance symptoms
• Slowly reintroducing these foods while monitoring your symptoms
• Calculating how much of a problem food you can tolerate and in what form
• Drawing up a long-term management plan for your food intolerance

Managing an elimination diet on your own can be tricky. There are hidden sources of food sensitivities in food and drink; for instance flavour enhancers or thickeners.^4,8 Your GP may refer you to a dietitian.

Managing food intolerance

People struggling with food intolerance often assume they’ll have to give up certain foods but you may only need to reduce how much you eat.⁸ The elimination diet can help pinpoint your tolerance level.¹ The idea is to keep foods on the menu where possible for nutritional balance, perhaps in smaller portions or different forms.^1,12,13

Although you may be able to drink small amounts of milk with meals, you may also find it easier to digest yoghurt or hard cheese. Lactase enzyme supplements from the health food shop may be helpful too.¹² Sourdough may also cause fewer symptoms than ordinary bread if your intolerant of gluten or FODMAPs.¹³

The most important thing is not to create nutritional gaps as that can have a significant impact on your health.¹

What exactly is a food allergy and how is it different from intolerance?

Unlike intolerance, food allergies are rooted in your immune system.¹ It defends your body against viruses, parasites, bacteria and other threats – and sometimes it overreacts. You eat something harmless and it produces antibodies called Immunoglobulin E (IgE). Eat the same food again and these antibodies could trigger an allergic reaction.¹⁴

Having the antibodies means you’re sensitised and not everyone goes on to develop the allergy. If you do, a tiny trace of your food allergen could be enough to trigger a reaction.¹ 

Symptoms of food allergy

Food allergy symptoms are the result of cells around your body releasing histamine and other chemicals in reaction to contact with your trigger.¹⁴ They usually start quickly and can be mild, moderate or severe, and even life-threatening.¹

There is another, less common, type of food allergic reaction that doesn’t involve IgE antibodies.^1,6,15 Symptoms can take several days to show and typically affect the gut and skin.⁶

Mild to moderate food allergy symptoms

People with food allergies tend to know they’ve eaten the wrong thing within minutes. It can take a couple of hours but the response is usually faster than with food intolerance, says national charity Allergy UK.^1,15 Symptoms can include:¹⁵

• Tingling or itching in the mouth
• A raised, itchy red rash (hives) – sometimes the skin can turn red and itchy but not raised
• Swelling of the face, mouth, throat or other parts of the body
• Difficulty swallowing
• Wheezing or shortness of breath
• Feeling dizzy and lightheaded
• Feeling sick (nausea) or vomiting
• Abdominal pain or diarrhoea
• Hay fever-like symptoms such as sneezing or itchy eyes

If you have a food allergy, it’s important to be aware that these symptoms can progress very quickly into life-threatening anaphylaxis.¹⁵ 

Severe food allergy symptoms: Anaphylaxis

Food allergy can cause a sudden severe allergic reaction that requires emergency medical treatment. It often begins with respiratory symptoms; in children, particularly, it can look like an asthma attack, says Resuscitation Council UK.¹⁶ Use an adrenaline device, if there’s one available, and dial 999:¹⁷

The signs and symptoms of an anaphylactic reaction can include:^16,17

• Difficulty breathing or breathing very fast, and noisily
• Persistent cough
• Hoarse voice
• Feeling drowsy, dizzy and confused
• Clammy, pale, even blue-tinged skin
• Collapsing or losing consciousness

Which food causes allergic reactions?

There are 14 foods considered by the Food Standards Agency to be major allergens: Peanuts, tree nuts, sesame seeds, soybeans, cereals containing gluten, eggs, milk, fish, crustaceans, molluscs, celeriac and celery, mustard, lupin and sulphites. By law, these must be highlighted on food packaging and restaurant menus if they are an ingredient.¹⁸

Certain plant-based foods may also cause symptoms but through a cross-reaction rather than a primary food allergy. The fruit, vegetable, spice or legume contains similar proteins to a certain pollen. For instance, someone who’s allergic to birch pollen may get a tingly mouth when they eat an apple. It’s called oral allergy syndrome and the effects are usually mild and local. But tell your doctor about it.¹⁹

Can you test for food allergies?

Yes, the common options are skin prick and blood tests. The first involves having drops of liquid containing possible allergy triggers on your arm and the skin gently pricked. A small itchy red bump after 15 minutes is a positive skin prick test result. Blood tests look for IgE antibodies.¹⁵

A skin prick test or a blood test can show if you’re sensitised to a substance. It doesn’t mean you have an allergy or will definitely develop one. It is up to your doctor to interpret the results for you and they may suggest an oral food challenge too. Be ready with details of your symptoms, medical history and any allergy in the family.¹⁵

Taking an allergy test won’t tell you whether you have a food intolerance (sensitivity).¹⁰

Treatments for food allergy vs intolerance

The treatment for food intolerance is modifying how much you eat of certain foods, in what form and how often.^1,12,13 With food allergy, you must avoid your trigger completely and may need short-term relief or emergency medication after accidental exposure.^14,15

• Mild to moderate food allergy symptoms: Antihistamine can block the effect of the histamine released by your body as part of an allergic reaction. There are many different types available over-the-counter so ask your pharmacist for advice.¹⁵
• Emergency medication: Your doctor will prescribe adrenaline for you to treat yourself in the event of anaphylaxis. Carry two adrenaline devices with you at all times and have an emergency action plan to share with people in your life who may need to help you.^15,16

If you have a food allergy or intolerance, your GP will have lots of advice to help you deal with your symptoms effectively.

The short version

Food allergy and intolerance are often confused but differ significantly. Allergies involve the immune system and can cause rapid, sometimes life-threatening reactions even to tiny amounts of the trigger.¹ Diagnosis uses skin prick or blood IgE tests, interpreted by your doctor – and possibly a food challenge. Symptoms include hives, swelling, breathing difficulties or, most severe of all, anaphylaxis. Managing food allergy requires strict avoidance and carrying emergency medication just in case.​¹⁵

Food intolerance does not involve the immune system and primarily affects the digestive system. Symptoms, like bloating, pain, diarrhoea or headache, are usually mild to moderate and depend on how much you’ve eaten.¹ A supervised elimination diet can help work out your problem food (there are tests for lactose intolerance) and adjusting your diet is the way to manage an intolerance.¹⁰ You may still be able to eat limited amounts.^1,10,12,13