Food Allergy

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

The symptoms of a food allergy almost always develop a few seconds or minutes after eating the food.

Some people may develop a severe allergic reaction (anaphylaxis), which can be life-threatening.

The most common type of allergic reaction to food is known as an IgE-mediated food allergy.

Symptoms include:

• tingling or itching in the mouth
• a raised, itchy red rash (urticaria) – in some cases, the skin can turn red and itchy, but without a raised rash
• swelling of the face, mouth (angioedema) or other areas of the body
• difficulty swallowing
• wheezing or shortness of breath
• feeling dizzy and lightheaded
• feeling sick (nausea) or vomiting
• abdominal pain or diarrhoea
• hay fever-like symptoms, such as sneezing or itchy eyes (allergic conjunctivitis)

Anaphylaxis

The symptoms of a severe allergic reaction (anaphylaxis) can be sudden and get worse very quickly.

Initial symptoms of anaphylaxis are often the same as those listed above and can lead to:

• increased breathing difficulties – such as wheezing and a cough
• a sudden and intense feeling of anxiety and fear
• a rapid heartbeat (tachycardia)
• a sharp and sudden drop in your blood pressure, which can make you feel light-headed and confused
• unconsciousness

Anaphylaxis is a medical emergency. Without quick treatment, it can be life-threatening. If you think you or someone you know is experiencing anaphylaxis, dial 999 and ask for an ambulance as soon as possible.

Non-IgE-mediated food allergy

Another type of allergic reaction is a non-IgE-mediated food allergy. The symptoms of this type of allergy can take much longer to develop – sometimes up to several days.

Some symptoms of a non IgE-mediated food allergy may be what you would expect to see in an allergic reaction, such as:

• redness and itchiness of the skin – although not a raised, itchy red rash (urticaria)
• the skin becomes itchy, red, dry and cracked (atopic eczema)

Other symptoms can be much less obvious and are sometimes thought of as being caused by something other than an allergy. They include:

• heartburn and indigestion that is caused by stomach acid leaking up out of the stomach (gastro-oesophageal reflux disease)
• stools (poo) becoming much more frequent or loose (though not necessarily diarrhoea)
• blood and mucus in the stools
• in babies: excessive and inconsolable crying, even though the baby is well-fed and doesn't need a nappy change (colic)
• constipation 
• redness around the anus, rectum and genitals
• unusually pale skin
• failure to grow at the expected rate

Mixed reaction

Some children can have a mixed reaction where they experience both "IgE" symptoms, such as swelling, and "non-IgE" symptoms, such as constipation.

This often happens to children who have a milk allergy.

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.

A food allergy is caused when your immune system mistakenly treats harmless proteins found in certain foods as a threat. It releases a number of chemicals, which then triggers an allergic reaction.

The immune system

The immune system protects the body by producing specialised proteins called antibodies.

Antibodies identify potential threats to your body, such as bacteria and viruses. They then signal to your immune system to release chemicals to kill the threat and prevent the spread of infection.

In the most common type of food allergy, an antibody known as immunoglobulin E (IgE) mistakenly targets a certain protein found in food as a threat. IgE can cause several chemicals to be released, the most important being histamine.

Histamine

Histamine causes most of the typical symptoms that occur during an allergic reaction. For example, histamine:

• causes small blood vessels to expand and the surrounding skin to become red and swell up
• affects nerves in the skin, causing itchiness
• increases the amount of mucus produced in your nose lining, which causes itching and a burning sensation

In most food allergies, the release of histamine is limited to certain parts of the body, such as your mouth, throat or skin.

In anaphylaxis, the immune system goes into overdrive and releases massive amounts of histamine and many other chemicals into your blood. This causes the wide range of symptoms associated with anaphylaxis.

Non-IgE-mediated food allergy

There is another type of food allergy, known as a non-IgE-mediated food allergy, caused by different cells in the immune system. This is much harder to diagnose as there is no test to accurately confirm non-IgE-mediated food allergy.

This type of reaction is largely confined to the skin and digestive system, causing symptoms such as heartburn, indigestion and eczema.

In babies, a non-IgE-mediated food allergy can also cause diarrhoea and reflux (stomach acid leaks up into the throat).

Foods

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

• eggs
• milk – if a child has an allergy to cow's milk, they are probably allergic to all types of milk, as well as infants' and follow-on formula
• soya
• wheat
• peanuts

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

However, any type of food can potentially cause an allergy.

Allergic reactions have been reported in association with:

• celery or celeriac – this can sometimes cause anaphylactic shock
• gluten – a type of protein found in cereals
• mustard
• sesame seeds
• fruit and vegetables – these usually only cause symptoms affecting the mouth, lips and throat (oral allergy syndrome)
• pine nuts (a type of seed)
• meat – some people are allergic to just one type of meat, while others are allergic to a range of meats; a common symptom is skin irritation

Who is at risk?

Exactly what causes the immune system to mistake harmless proteins as a threat is unclear. However, a number of risk factors for food allergies have been identified, which are outlined below.

Family history

If you have a parent, brother or sister with an allergic condition – such as asthma, eczema or a food allergy – you have a slightly higher risk of developing a food allergy. However, you may not develop the same food allergy as your family members.

Other allergic conditions

Children who have atopic dermatitis (eczema) in early life are more likely to develop a food allergy.

The rise in food allergy cases

The number of people with food allergies has risen sharply over the past few decades, although the reason is unclear. For example, the number of children admitted to hospital for food-related anaphylaxis since 1990 has risen seven-fold.

One theory behind the rise is that a typical child’s diet has changed considerably over the last 30 to 40 years.

Another theory is that children are increasingly growing up in "germ-free" environments. This means that their immune systems may not receive sufficient early exposure to the germs needed to develop properly. This is known as the hygiene hypothesis.

Food additives

It is rare for someone to have an allergic reaction to food additives. However, certain additives may cause a flare-up of symptoms in people with pre-existing conditions.

Sulphites

Sulphur dioxide (E220) and other sulphites (E221, E222, E223, E224, E226, E227 and E228) are used as preservatives in a wide range of foods, especially soft drinks, sausages, burgers, and dried fruits and vegetables.

Sulphur dioxide is produced naturally when wine and beer are made. It is often added to wine to stop it from continuing to ferment in the bottle. Usually, most of the "head space" in a bottle of wine (the part of the bottle not filled with wine) is sulphur dioxide.

Anyone who has asthma or allergic rhinitis may react to inhaling sulphur dioxide. A few people with asthma have had an attack after drinking acidic drinks containing sulphites, but this is not thought to be very common.

Food labelling rules require pre-packed food sold in the UK, and the rest of the European Union, to show clearly on the label if it contains sulphur dioxide or sulphites at levels above 10mg per kg or per litre.

Benzoates

Benzoic acid (E210) and other benzoates (E211, E212, E213, E214, E215, E218 and E219) are used as food preservatives to prevent yeasts and moulds from growing, most commonly in soft drinks. They occur naturally in fruit and honey.

Benzoates could make the symptoms of asthma and eczema worse in children who already have these conditions.

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.

Allergy UK has more information on oral allergy syndrome.

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.

Read more about identifying foods that cause allergies (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.

There are two main types of medication that can be used to relieve the symptoms of an allergic reaction to foods:

• antihistamines, which can be used to treat mild to moderate allergic reaction
• adrenaline, which can be used to treat severe allergic reactions (anaphylaxis)

Antihistamines

Antihistamines work by blocking the effects of histamine, which is responsible for many of the symptoms of an allergic reaction.

Many antihistamines are available from your pharmacist without prescription – stock up in case of an emergency. Non-drowsy antihistamines are preferred.

Some antihistamines, such as alimemazine and promethazine, aren't suitable for children under two years old. If you have a younger child with a food allergy, ask your GP about what types of antihistamines may be suitable.

Avoid drinking alcohol after taking an antihistamine as this can make you feel drowsy.

Adrenaline

Adrenaline works by narrowing the blood vessels to counteract the effects of low blood pressure, and by opening up the airways to help ease breathing difficulties.

If you or your child is at risk of anaphylaxis or has had a previous episode of anaphylaxis, you will be given an auto-injector of adrenaline to use in case of emergencies.

Carefully read the manufacturer’s instructions that come with the auto-injector and when your child is old enough, train them how to use it (see below).

Using an auto-injector

If you suspect that somebody is experiencing the symptoms of anaphylaxis, call 999 and ask for an ambulance. Tell the operator that you think the person has anaphylaxis.

Older children and adults will probably have been trained to inject themselves. You may need to inject younger children, or older children and adults who are too sick to inject themselves.

There are three types of auto-injectors:

• EpiPen
• Anapen
• Jext

All three work in much the same way. If anaphylaxis is suspected, you should remove the safety cap from the injector, place it against your outer thigh (holding it at a right angle) and hold down the firing button at the end of the injector. The injections can be given through clothing.

This will send a needle into your thigh and deliver a dose of adrenaline. You need to hold down the button for 10 seconds.

If the person is unconscious, check their airways are open and clear, and check their breathing. Then put them in the recovery position (see below). Putting someone who is unconscious in the recovery position ensures they do not choke on their vomit.

Place the person on their side, making sure they are supported by one leg and one arm. Open the airway by tilting the head and lifting the chin.

If the person's breathing or heart stops, cardiopulmonary resuscitation (CPR) should be performed.

Owning an auto-injector

As a precaution, the following advice should be taken: 

• Carry the auto-injector at all times or encourage your child to do so if they are old enough. You may be recommended to carry multiple injectors – check with your GP or the doctor in charge of your care. You may also be given an emergency card or bracelet with full details of your child’s allergy and contact details of their doctor, to alert others. They should wear this at all times.
• Extreme temperatures can make adrenaline less effective. Do not leave an auto-injector in places such as your fridge or the glove compartment of your car.
• Check the expiry date regularly. EpiPen and Jext have a shelf life of 18 months after the date of manufacture, and Anapen has a shelf life of two years. An out-of-date injector will only offer limited protection.
• The manufacturers offer a reminder service, where you can be contacted near the date of expiry. Check the information leaflet that comes with the medication for more information.
• If your child has an auto-injector, they will need to change over to an adult dose once they reach a weight of 30 kilos (4.7 stone). Depending on the shape and size of your child’s body, this could be anywhere between the ages of 5 and 11 years old.
• Do not delay injecting if you think you or your child may be experiencing the start of anaphylaxis, even if the initial symptoms are mild. It's better to use adrenaline early and find out it was a false alarm than delay treatment until you are sure your child is experiencing severe anaphylaxis. 

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.