What is a food allergy?

There are an estimated two million people in the UK living with a diagnosed food allergy with approximately 6-8% of children under three affected by food allergens [1].  So, let’s get down to basics – what is a food allergy and what’s the difference between an immediate and a delayed allergy?

A food allergy occurs when your body makes a mistake and identifies certain foods as potentially harmful. This means your immune system kicks in and causes an allergic reaction.

Doctors don’t really know why some people’s bodies respond in this way but the number of us affected is growing.

Whilst people can be allergic to any food, 90% of allergic reactions are caused by just 9 types of food:  milk, eggs, soya, peanuts, tree nuts, wheat, sesame, fish and shellfish.  Foods that cause allergic reactions are called allergens.  Some people will only react to one allergen, others will be allergic to multiple foods. If you’ve got one allergy, you’re more likely to have others.

Allergies are more common in children than in adults. Fortunately, children often outgrow their food allergies but it’s also possible to develop new allergies in adulthood.

Types of food allergy

There are two types of food allergy: immediate food allergy and delayed food allergy.

Immediate food allergy is also known as IgE-mediated. It involves the fast-acting part of the immune system. When it identifies an allergen, the immune system releases a chemical called histamine which causes symptoms such as itchiness, a rash or swelling. In more severe cases it can cause abdominal pain and sometimes anaphylaxis. Anaphylaxis is a life-threatening allergic reaction which involves either difficulty breathing or a problem with blood circulation.

Delayed food allergy is also known as non-IgE-mediated. It involves a slower acting part of your immune system. It is not as dangerous but it can cause unpleasant symptoms, including gastrointestinal problems such as diarrhoea or reflux, or skin problems, such as eczema.

IgE stands for immunoglobulin E, the antibody which causes allergic reactions.

Professor Adam Fox explains what IgE is

Which foods cause allergic reactions?

Remember, you can be allergic to any food but there are 14 main allergens recognised by the UK and EU: milk, eggs, peanuts, tree nutssoyawheat and other cereals containing gluten, fish, crustaceans, molluscs, mustard, lupin, sulphites, sesame and celery. By law, all food manufacturers need to label these 14 main allergens in their ingredient lists.  For more information about each of these please take a look at our factsheets.

What can you do about a food allergy?

If you suspect a food allergy you should go and see your GP.  The best way to prevent an allergic reaction is to avoid the food causing the allergy.  This means cutting this food, and any of its derivatives, from your or your child’s diet.  It’s important to do this with advice from a doctor and dietitian as some foods, such as milk, contain important nutrients.

Feeling anxious? Don’t worry, you’re not alone.

We understand that learning about food allergies can feel daunting. Arming yourself with information can help relieve anxiety; and there are other tips in Emma Amascato’s piece about allergies and anxiety here.


Written by: The Allergy Team, 15th March 2021

Reviewed by:
Dr Neeta Patel, Consultant Paediatrician and Allergy Lead
Dr David Mass, GP with a special interest in allergy


[1] Guys and St Thomas’ NHS Foundation Trust
Food allergy – NHS

Disclaimer: All information provided by The Allergy Team Ltd is general information only.  Please contact your GP or other qualified healthcare professionals for specific advice.