Food Allergy and Food Intolerance

Food allergy and food intolerance - common food allergens

Having to avoid certain foods in your diet can be difficult. But there are a few simple things you can do to help you manage your food allergies - allowing you to stay safe, continue to participate in fun activities and enjoy your food. 

What is the difference between food allergy and food intolerance?

For some people, eating certain foods can lead to an unpleasant and sometimes dangerous physical reaction.

The term used to describe all types of reactions to foods is ‘food hypersensitivity’. A 'food allergy' is a reaction involving the immune system (the body’s defence against foreign bodies). Those that do not involve the immune system are often called a ‘food intolerance’.

It is important to identify and manage foods that trigger any symptoms in an appropriate way.

Food allergy

Proteins within foods can trigger immediate (within two hours) or delayed symptoms (up to several days later).

Immediate food allergy (IgE mediated food allergy)

Immediate reactions to foods occur when your immune system reacts to a normally harmless protein in food, due to the creation of Immunoglobulin E (IgE).

This results in the release of chemicals (e.g. histamine) which trigger allergic symptoms. These symptoms are usually in the skin (itching/swelling), or gut (vomiting, diarrhoea).

Other symptoms can include breathing problems and in rare cases an extreme allergic reaction called anaphylaxis.

Delayed food allergy (non IgE mediated food allergy)

Delayed reactions to foods still involve your immune system, but there is a different type of immune reaction involved. Symptoms typically occur in the gut (vomiting, diarrhoea, constipation) and/or the skin (atopic eczema).

Which foods are involved?

The most common foods to be involved in children's allergy are:

  1. cow’s milk
  2. hen’s eggs
  3. peanuts
  4. tree nuts e.g. hazelnuts, almonds, walnuts, Brazil nuts, cashew and pistachio nuts
  5. wheat
  6. soya
  7. fish
  8. shellfish, especially prawns
  9. sesame

In adults, the most common type of food allergy is to raw fruits and raw vegetables. It is known as pollen food syndrome. Fish, shellfish, legumes and seeds are also common causes of allergy in adults.

Food allergy testing

If you think you have a food allergy, you will need specialist input to diagnose your allergy and help you manage it. For more information see the Food Allergy and Intolerance Testing fact sheet.

Food intolerance

There are many different types of ‘food intolerance’. Food intolerances do not involve your immune system. Reactions often show a vast range of symptoms, and can be individual to you. 

The onset of reactions could be immediate or delayed and the symptoms range in severity. If you think you have a food intolerance, you will need a detailed clinical history by an experienced healthcare professional to diagnose and help you manage these reactions.

Lactose intolerance

This is one of the most common food intolerances. It occurs when you have either too little or no lactase. This is the enzyme which helps to digest lactose, the sugar found in milk and dairy products from all types of animals (such as cow, goat and sheep).

If you are lactose intolerant you should avoid or reduce these foods. Replace them with lactose-free milk and dairy products or fortified plant-based alternatives.

Histamine intolerance

This is a reaction to certain naturally occurring substances in foods called vaso-active amines – such as histamine. Common trigger foods include red wine, strong and blue cheeses, tuna, mackerel, pork products, tomatoes and various other preserved foods.

Salicylate sensitivity

Salicylates are substances, chemically similar to aspirin, found in a wide variety of plant foods. Some fruits, vegetables, nuts, herbs and spices are high in salicylates. Most people can tolerate small amounts of these foods.

Other sensitivities

Some people can have reactions to caffeine or theobromine - found in chocolate.

There are also many reactions to foods with unknown mechanisms such as intolerance to food additives benzoate and sulphite, preservatives and monosodium glutamate.

In all these examples avoidance of foods or reduced intake may improve the symptoms. Often there can be other factors that also need to be considered.

Food labelling

Under UK law, food businesses must inform you if they use any of the 14 allergens as ingredients in the food and drink they provide. The 14 allergens are: celery, cereals containing gluten (such as rye, wheat, barley and oats), crustaceans (such as prawns, crabs and lobsters), eggs, fish, lupin, milk, molluscs (such as mussels and oysters), mustard, peanuts, sesame, soybeans, sulphur dioxide (sulphites) and tree nuts (such as almonds, hazelnuts, walnuts, brazil nuts, cashews, pecans, pistachios and macadamia nuts).

Prepacked food - Allergens must be emphasised within the ingredients list of pre-packed food or drink, for example on tins you buy in the supermarket. This could be done by using bold, italic or coloured type.

Non-prepacked (loose) food - Food businesses such as a bakery, butchers or delicatessen, must provide you with allergen information for any loose item you buy that contains any of the 14 allergens.

Foods prepacked for direct sale (PPDS) – These are foods packed and prepared on the same site, such as in a café, sandwich shop, deli or food outlet preparing food in their own kitchen. From 1 October 2021, PPDS food must have a label that displays a full ingredients list. The 14 allergens must be emphasised within it.

Eating out – A restaurant or café must provide you with allergen information in writing. This could be allergen information on their menu or a written notice explaining how you can get this information. Ask a member of staff about the allergen content of a dish you wish to order.

Food delivery & takeaway food - If you are ordering food online or by phone, allergen information must be provided before purchase is completed and when the food is delivered (in writing or verbally). If ordering through a food delivery company you must contact the restaurant directly.

Precautionary allergen labelling - ‘May contain’ statements are often used on food packaging to state that a food may be contaminated with one of the common allergens. There is no law to say when these statements should be used. This type of labelling is used on many foods, so it is important to discuss the safest approach with your doctor or dietitian.

Top tips

  • When a food hypersensitivity reaction involves the immune system, it is called a ‘food allergy’. If it does not involve the immune system, it is often called a ‘food intolerance’ or an ‘adverse reaction’.
  • If you have to cut out complete food groups from your diet such as dairy or wheat, try to make sure the foods you replace them with have enough of the nutrients you need.
  • Look out for, and try, new ‘free from’ products as this will help add variety and enjoyment to your diet. These are clearly labelled and are common foods made without the standard ingredients.
  • Develop your cooking skills! Adapt your favourite recipes using suitable alternative ingredients.
  • Plan ahead. For special occasions or meals out, let your host or chef know your dietary requirements.
  • Prepare in advance for holidays abroad. This includes emergency medication, translation cards and making your airline and accommodation aware.
  • Be aware of the ingredients used in cuisines from different countries.
  • Know your level of food avoidance. Find out if you have to avoid tiny ‘trace’ amounts of food allergens or if you can have small amounts without triggering a reaction. Be aware of the risk of cross-contamination on surfaces and utensils.
  • Always carry the emergency medication recommended by your doctor. Make sure your family and friends know what to do in an emergency.
  • If you are unsure about which foods you can and can’t eat and need further dietary advice, ask your doctor to refer you to a dietitian.


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