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Overview - Food Allergy

A food allergy is when the body's immune system reacts to specific foods. Although allergic reactions are often mild, they can be serious.


Symptoms can affect different areas of the body at the same time.

Some common symptoms include:

  • an itchy sensation inside the mouth, throat or ears
  • a raised itchy red rash (urticaria, or hives)
  • swelling of the face, around the eyes, lips, tongue and roof of the mouth (angioedema)
  • vomiting

There are different types of food allergies, which come with different symptoms.

Find out more about food allergy symptoms


In the most serious cases a person may have a severe allergic reaction (anaphylaxis). This can be life threatening.

Emergency action required: Call 112 or 999 if

you think someone has symptoms of anaphylaxis, such as:

  • breathing difficulties
  • trouble swallowing or speaking
  • feeling dizzy or faint

Ask for an ambulance and tell the operator you think the person is having a severe allergic reaction.

Causes of food allergies

Food allergies happen when the immune system mistakenly treats proteins found in food as a threat. The immune system is the body's defence against infection.

As a result, some chemicals are released. These chemicals cause the symptoms of an allergic reaction.

Almost any food can cause an allergic reaction. There are certain foods that are responsible for most food allergies.

In children

Most food allergies affect children under the age of 3. Many children will grow out of the allergy by the time they start school.

In children, the foods that most commonly cause an allergic reaction are:

  • milk
  • eggs
  • peanuts
  • tree nuts
  • fish
  • shellfish

Peanut and tree nut allergies usually last longer. Around 4 out of 5 children with peanut allergies remain allergic for the rest of their lives.

Most children that have a food allergy will have had eczema during infancy. The worse the child's eczema and the earlier it started, the more likely they are to have a food allergy.

In adults

Allergies that develop in adulthood, or persist into adulthood, are often lifelong allergies.

In adults, the foods that most commonly cause an allergic reaction are:

  • peanuts
  • tree nuts
  • fruits
  • fish
  • shellfish

Find out more about food allergy causes and risk factors

Types of food allergies

Food allergies are divided into 3 types, depending on symptoms and when they happen.

IgE-mediated food allergy

This is the most common type. It is triggered by the immune system producing an antibody called immunoglobulin E (IgE). Symptoms develop a few seconds or minutes after eating. There's a greater risk of anaphylaxis with this type of allergy.

Non-IgE-mediated food allergy

These allergic reactions are not caused by immunoglobulin E, but by other cells in the immune system. This type of allergy is often hard to diagnose as symptoms take much longer to develop (up to several hours).

Mixed IgE and non-IgE-mediated food allergies

Some people may experience symptoms from both types.

Oral allergy syndrome (pollen-food syndrome)

Some people experience itchiness in their mouth and throat after eating fresh fruit or vegetables. They might also experience mild swelling. This is known as oral allergy syndrome.

Oral allergy syndrome is caused by allergy antibodies mistaking certain proteins in food for pollen.

Oral allergy syndrome generally does not cause severe symptoms. It's possible to deactivate the allergens by cooking any fruit and vegetables.


The best way to prevent an allergic reaction is to identify the food that causes the allergy and avoid it.

Talk to your GP before making any radical dietary changes.

Medicine called antihistamines can relieve the symptoms of an allergic reaction.

Adrenaline is an effective treatment for more severe allergic symptoms, such as anaphylaxis. You may be given a device known as an auto-injector pen to use in emergencies.

Find out more about treatment of food allergies

When to contact a GP

Non-urgent advice: Talk to your GP if:

  • you think you or your child may have a food allergy

They can refer you to an allergy clinic. Commercial allergy testing kits are not recommended.

Find out more about diagnosing food allergies

Food intolerance

A food intolerance is not the same as a food allergy. An intolerance is when you have difficulty digesting certain substances but no allergic reaction takes place. People with food intolerance may have diarrhoea, bloating, and stomach cramps.

Important differences between a food allergy and a food intolerance include:

  • the symptoms of a food intolerance usually happen several hours after eating the food
  • you need to eat a larger amount of food to trigger an intolerance than an allergy
  • a food intolerance is never life threatening, unlike an allergy

Content supplied by the NHS and adapted for Ireland by the HSE

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This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.

Page last reviewed: 13 March 2021
Next review due: 13 March 2024