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)
There are different types of food allergies, which come with different symptoms.
In the most serious cases, a person has a severe allergic reaction (anaphylaxis), which can be life threatening.
Immediate action required: Call 999 or 112 if you think someone has the 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.
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:
- tree nuts
Peanut and tree nut allergies are usually more persistent. 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 experienced eczema during infancy. The worse the child's eczema and the earlier it started, the more likely they are to have a food allergy.
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:
- tree nuts
Types of food allergies
Food allergies are divided into 3 types, depending on symptoms and when they occur.
IgE-mediated food allergy
The most common type, triggered by the immune system producing an antibody called immunoglobulin E (IgE). Symptoms occur 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 difficult 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.
Medication 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.
When to contact a GP
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.
A food intolerance is not the same as a food allergy. An intolerance is 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