Food allergy

Introduction 

A food allergy is when the body's immune system reacts unusually to specific foods. Allergic reactions are often mild, but they can sometimes be very serious.

In young children, common food allergies include milk and eggs. In adults, allergies to fruit and vegetables are more common. Nut allergies, including peanuts, are relatively common in both school-age children and adults.

Symptoms of a food allergy 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 (known as urticaria or hives)
• swelling of the face, around the eyes, lips, tongue and roof of the mouth (known as angioedema)
• vomiting

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Anaphylaxis

In the most serious cases, a person has a severe allergic reaction (anaphylaxis), which can be life-threatening.

If you think someone has the symptoms of anaphylaxis – such as breathing difficulties, lightheadedness and feeling like they are going to faint or lose consciousness – call 999, ask for an ambulance and tell the operator you think the person has anaphylaxis or "anaphylactic shock".

What causes food allergies?

Food allergies happen when the immune system (the body’s defence against infection) mistakenly treats proteins found in food as a threat.

As a result, a number of chemicals are released. It is these chemicals that cause the symptoms of an allergic reaction.

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

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

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

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.

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

• peanuts
• tree nuts – such as walnuts, brazil nuts, almonds and pistachios
• fish
• crustaceans (shellfish) – such as crab, lobster and prawns

It's still unknown why people develop allergies to food, although they often have other allergic conditions, such as asthma, hay fever and eczema.

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.

Types of food allergies

Food allergies are divided into three 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 is 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

Some people experience itchiness in their mouth and throat (sometimes with mild swelling) immediately after eating fresh fruit or vegetables. This is known as oral allergy syndrome.

Oral allergy syndrome is not a true food allergy. It is caused by allergy antibodies mistaking certain proteins in fresh fruits, nuts or vegetables for pollen.

Oral allergy syndrome generally does not cause severe symptoms, and it is possible to deactivate the allergens by thoroughly cooking any fruit and vegetables.

Treatment

There is no treatment to cure a food allergy. The best way of preventing an allergic reaction is to identify the food that causes the allergy and then avoid it.

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 (these are known as allergens).

However, avoid making any radical changes to your or your child’s diet, such as cutting dairy products, without first talking to your GP. You should speak to a dietician before making any changes.

A type of medication called an antihistamine can help relieve the symptoms of a mild or moderate allergic reaction. A higher dose of antihistamines is often needed to control symptoms.

Adrenaline is also an effective treatment for anaphylaxis.

People with a food allergy are often given a device, known as an auto-injector pen, which contains doses of adrenaline that can be used in emergencies.

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When to seek medical advice

If you think you or your child may have a food allergy, it's very important to ask for a professional diagnosis from your GP. They can then refer you to an allergy clinic.

Many parents mistakenly assume their child has a food allergy, when their symptoms are actually due to a completely different condition.

Commercial allergy-testing kits are available, but their use is not recommended. Many kits are based on unsound scientific principles. Even if they are reliable, you should have the results looked at by a health professional.

Who is affected

Most food allergies affect younger children aged under the age of three. It is estimated that around one in every 14 children of this age has at least one food allergy.

Most children who have food allergies to milk, eggs, soya and wheat in early life will "outgrow" this allergy by the time they start school.

Peanut and tree-nut allergies are usually more persistent. An estimated four out of five children with peanut allergies remain allergic to peanuts for the rest of their lives.

Food allergies that develop during adulthood, or persist into adulthood, are likely to be lifelong allergies.

For reasons that are unclear, rates of food allergies have risen sharply in the last 20 years.

However, deaths from anaphylaxis-related food reactions are now very rare. There are around 10 deaths related to food allergies in England and Wales each year.

Food allergy and intolerance myth buster

There are many myths about food allergies and intolerances – can you tell fact from fiction? And what is the difference between the two? 

What is 'food intolerance'?

A food intolerance is not the same as a food allergy.

People with food intolerance may have symptoms such as diarrhoea, bloating and stomach cramps. This may be caused by difficulties digesting certain substances, such as lactose. However, no allergic reaction takes place.

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

• The symptoms of a food intolerance usually occur 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.

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