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There are an estimated two million people in the UK living with a diagnosed food allergy and approximately 6-8% of children under three are affected[1]But what is a food allergy and what are the symptoms of an allergic reaction?

What is a food allergy?

A food allergy occurs when your body mistakenly identifies certain foods as harmful, triggering a response by your immune system. 

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

You can be allergic to any food but 90% of allergic reactions are caused by just 9 foods:  milk, eggs, soya, peanuts, tree nuts, wheat, sesame, fish and shellfish.  Foods which 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 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.

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, soya, eggs, cereals containing gluten, fish, molluscs, crustaceans, tree nuts, peanuts, sesame, celery, lupin, mustard and sulphites.  By law, all food manufacturers need to label these 14 main allergens in their list of ingredients.

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 you 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 which need to be replaced.

Symptoms of an allergic reaction

Symptoms of an allergic reaction differ depending on whether you have an immediate or delayed food allergy.

Some people will only experience mild symptoms, but others can suffer more serious reactions. The most severe type of allergic reaction is called anaphylaxis and it can be life-threatening.

Understanding the symptoms and knowing when to seek help is really important.

Immediate food allergy symptoms – symptoms usually start as soon as you eat or drink the food that you are allergic to, but can begin up to 2 hours after.  They can include:

Mild symptoms:

  • Tingling or itching in the mouth
  • An itchy red rash (known as hives) – sometimes this is raised but not always, and can look like stinging nettle rash
  • Swelling of the face, such as lips and eyes
  • Sneezing or itchy eyes
  • Feeling sick or vomiting
  • Stomach pain or diarrhoea
  • Eczema

Severe symptoms (which can be signs of anaphylaxis):

  • Hoarse voice, difficulty speaking or swallowing
  • Swollen tongue
  • Difficulty breathing, tight chest, wheezing or shortness of breath
  • Feeling dizzy or lightheaded
  • Persistent cough
  • Floppiness or collapse


Anaphylaxis is a very severe allergic reaction which can affect a person’s breathing or circulatory system. It can be fatal and should be treated as a medical emergency.

People with food allergies who are at risk of anaphylaxis are usually prescribed adrenaline which is delivered via a pen-like device called an adrenaline auto-injector. There are three brands in the UK: EpiPen, JEXT and Emerade.

If you suspect someone is suffering anaphylaxis always give adrenaline first and then call 999.

Leading paediatric allergy consultant, Professor Adam Fox says: “If you’ve been prescribed an adrenaline auto-injector…this is the time to use it. Or if you’re not sure if the reaction is bad enough, you’re better to just get on and use it anyway, or if you don’t have one of those, call for help.”

Details of how to administer adrenaline can be found on the NHS website here.

Delayed food allergy symptoms

Signs of a delayed allergy can take longer to appear and can be harder to identify and diagnose than an immediate food allergy.  Symptoms can include:

  • Worsening of eczema
  • Changes in bowel pattern e.g., watery poo (stools) or constipation
  • Gastric problems such as reflux, tummy ache
  • Lack of weight gain and excessive irritability or inconsolable crying in babies


Food allergy – NHS (