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’s 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 hazelnuts
• fruits – such as apples and peaches
• fish
• 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.

Read more information about the causes and risk factors for food allergies

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’s a greater risk of anaphylaxis with this type of allergy.
• non-IgE-mediated food allergy – these allergic reactions aren’t 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.

Read more information about the symptoms of a food allergy

Oral allergy syndrome (pollen-food 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 caused by allergy antibodies mistaking certain proteins in fresh fruits, nuts or vegetables for pollen.

Oral allergy syndrome generally doesn’t cause severe symptoms, and it’s possible to deactivate the allergens by thoroughly cooking any fruit and vegetables.

Some people with pollen-food syndrome may have more severe symptoms.

The Allergy UK website has more information on oral allergy syndrome.

Treatment

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

Research is currently looking at ways to desensitise some food allergens, such as peanuts and milk, but this is not an established treatment.

Read more about identifying foods that cause allergies (allergens)

Avoid making any radical changes, such as cutting out dairy products, to your or your child’s diet without first talking to your GP. For some foods, such as milk, you may need to speak to a dietitian 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 antihistamine is often needed to control acute allergic symptoms.

Adrenaline is an effective treatment for more severe allergic symptoms, such as 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.

Read more about the treatment of food allergies

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 if appropriate.

Many parents mistakenly assume their child has a food allergy when their symptoms are actually caused by a completely different condition.

Commercial allergy testing kits are available, but using them isn’t recommended. Many kits are based on unsound scientific principles. Even if they’re reliable, you should have the results looked at by a health professional.

Read more about diagnosing food allergies

Who’s affected?

Most food allergies affect younger children under the age of three. It’s estimated around 1 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 grow out of it 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 rare.