Food allergy

A food allergy happens when the body's immune system reacts in an unusual way to certain foods. Allergic reactions are often mild, but they can be very serious.

The symptoms of a food allergy can affect several parts of the body at the same time. Some common ones are:

• an itchy feeling 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

In the most serious cases of food allergy, a person has a severe allergic reaction called anaphylaxis, and this can be life threatening.

If you think someone has the symptoms of anaphylaxis, call 999. These symptoms include breathing difficulties, lightheadedness, and feeling like they're going to faint or lose consciousness.

Ask for an ambulance and tell the operator you think the person has anaphylaxis or "anaphylactic shock".

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 certain foods 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 who 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, 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.

Food allergy comes in three types, and doctors tell them apart by the symptoms and by when those symptoms appear.

• IgE-mediated food allergy is the most common type. It is triggered when the immune system makes an antibody called immunoglobulin E (IgE). Symptoms come on a few seconds or minutes after eating, and the risk of anaphylaxis is greater with this type.
• Non-IgE-mediated food allergy isn't caused by immunoglobulin E but by other cells in the immune system. It is often difficult to diagnose, because symptoms take much longer to develop (up to several hours).
• Mixed IgE and non-IgE-mediated food allergy means some people have symptoms from both types.

Some people get an itchy mouth and throat, sometimes with mild swelling, straight after eating fresh fruit or vegetables. This is called oral allergy syndrome.

The cause is that allergy antibodies mistake certain proteins in fresh fruits, nuts or vegetables for pollen.

Oral allergy syndrome doesn't usually cause severe symptoms, and thoroughly cooking the fruit and vegetables can deactivate the allergens. Some people with pollen-food syndrome, though, may have more severe symptoms.

The best way to prevent an allergic reaction is to find out which food causes your food allergy and avoid it. Researchers are looking at ways to desensitise people to some food allergens, such as peanuts and milk, but this is not an established treatment yet.

Don't make any radical changes to your or your child's diet, such as cutting out dairy products, without first talking to your doctor. For some foods, such as milk, you may need to speak to a dietitian before changing anything.

A type of medicine 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 called an auto-injector pen, which contains doses of adrenaline that can be used in emergencies.

If you think you or your child may have a food allergy, it's very important to see a doctor for a proper diagnosis. The doctor can then refer you to an allergy clinic if that's appropriate.

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

Allergy testing kits are sold commercially, but using them isn't recommended. Many of the kits are based on unsound scientific principles. Even if a kit is reliable, you should still have the results looked at by a health professional.

Food allergy mostly affects young children, especially those under the age of three. An estimated 1 in every 14 children of this age has at least one food allergy.

Most children who are allergic to milk, eggs, soya or wheat in early life will grow out of it by the time they start school.

Peanut and tree nut allergies tend to last longer. An estimated four out of five children with a peanut allergy stay allergic to peanuts for the rest of their lives.

If a food allergy develops in adulthood, or carries on into adulthood, it is likely to be lifelong.

Nobody is clear why, but rates of food allergy have risen sharply in the last 20 years. The good news is that deaths from anaphylaxis-related food reactions are now rare.

A food allergy almost always shows itself within a few seconds or minutes of eating the food. Some people have a severe allergic reaction (anaphylaxis), which can be life threatening.

The most common kind of allergic reaction to food is called an IgE-mediated food allergy. The symptoms include:

• tingling or itching in the mouth
• a raised, itchy red rash (urticarial). In some cases the skin turns red and itchy, but without a raised rash
• swelling of the face, mouth (angioedema), throat 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 conjunctivitus)

A severe allergic reaction, called anaphylaxis, can come on suddenly and get worse very quickly.

The first symptoms are often the same as those listed above, but they can go on to cause:

• more difficulty breathing, such as wheezing and a cough
• a sudden, intense feeling of anxiety and fear
• a rapid heartbeat (tachycardia)
• a sharp and sudden drop in your blood pressure, which can make you feel lightheaded 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 having anaphylaxis, dial 999 and ask for an ambulance as soon as possible.

Non-IgE-mediated food allergy is another type of allergic reaction. The symptoms can take much longer to show up, sometimes up to several days.

Some symptoms are what you'd expect to see in an allergic reaction, such as:

• redness and itchiness of the skin, though not a raised, itchy red rash (urticarial)
• skin that becomes itchy, red, dry and cracked (atopic eczema)

Other symptoms are much less obvious, and people sometimes think something other than an allergy is causing them. They include:

• heartburn and indigestion caused by stomach acid leaking up out of the stomach (gastro-oesophageal reflux disease)
• stools (faeces) 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

Some children have a mixed reaction to a food, which means they show both IgE symptoms, such as swelling, and non-IgE symptoms, such as constipation. A child with a milk allergy can react in this way.

A food allergy happens when your immune system treats harmless proteins in certain foods as a threat. It then releases a number of chemicals, and these trigger an allergic reaction.

Your immune system protects your body by making special proteins called antibodies. These antibodies spot possible threats, such as bacteria and viruses. They then signal the immune system to release chemicals that kill the threat and stop an infection from spreading.

In the most common type of food allergy, an antibody called immunoglobulin E (IgE) wrongly treats a certain protein in food as a threat. IgE can cause several chemicals to be released, and the most important of these is histamine.

Histamine is behind most of the typical symptoms you get during a food allergy reaction. Here is what it does:

• It makes small blood vessels expand, so the skin around them turns red and swells up
• It affects the nerves in your skin, which causes itchiness
• It increases the amount of mucus made in the lining of your nose, which causes itching and a burning sensation

In most food allergies, the histamine is released only in certain parts of the body, such as your mouth, throat or skin.

Anaphylaxis is different. The immune system goes into overdrive and pours huge amounts of histamine, along with many other chemicals, into your blood. That is what causes the wide range of symptoms linked with anaphylaxis.

There's another type of food allergy, called non-IgE-mediated food allergy, and it's caused by different cells in the immune system. It is much harder to diagnose, because there's no test that can accurately confirm it.

This type of reaction mostly stays in the skin and the digestive system. It can cause symptoms such as heartburn, indigestion and eczema.

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

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

• eggs
• milk (if a child is allergic to cow's milk, they're 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
• 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, known as 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)

No one knows exactly why the immune system mistakes harmless proteins for a threat in a food allergy. But doctors have found a number of risk factors for food allergies, and they are outlined below.

If your parent, brother or sister has an allergic condition, such as asthma, eczema or a food allergy, your own risk of developing a food allergy is slightly higher. But you may not end up with the same food allergy as your family members.

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

The number of people with food allergy has risen sharply over the past few decades. Nobody is sure why, though other allergic conditions, such as atopic dermatitis, have also become more common.

One theory is that a typical child's diet has changed a great deal over the last 30 to 40 years.

Another theory is that more and more children are growing up in "germ-free" surroundings. If that's so, their immune systems may not meet enough germs early in life, and those germs are needed for the immune system to develop properly. This idea is known as the hygiene hypothesis.

Allergic reactions to food additives are rare. But some additives can set off a flare-up of symptoms in people who already have certain conditions.

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

Sulphur dioxide is produced naturally when wine and beer are made, and it's sometimes added to wine. 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 isn't thought to be very common.

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

Benzoic acid (E210) and other benzoates (E211, E212, E213, E214, E215, E218 and E219) are added to food as preservatives, to stop yeasts and moulds from growing. You'll find them most often in soft drinks. Benzoates also occur naturally in fruit and honey.

Children who already have asthma or eczema may find their symptoms get worse after benzoates.

If you think you or your child has a food allergy, make an appointment with your doctor.

The doctor will ask you some questions about the pattern of your child's symptoms, such as:

• how long did it take for the symptoms to start after exposure to the food?
• how long did the symptoms last?
• how severe were the symptoms?
• is this the first time these symptoms have occurred? If not, how often have they occurred?
• what food was involved and how much of it did your child eat?

They'll also want to know about your child's medical history, such as:

• do they have any other allergies or allergic conditions?
• is there a history of allergies in the family?
• was (or is) your child breastfed or bottle-fed?

The doctor may also check your child's weight and size, to make sure they're growing at the expected rate.

If your doctor suspects a food allergy, you may be referred to an allergy clinic or centre for testing. The tests you need can vary, depending on the type of allergy:

• if your symptoms developed quickly (an IgE-mediated food allergy), you'll probably be given a skin-prick test or a blood test
• if your symptoms developed more slowly (a non-IgE-mediated food allergy), you'll probably be put on a food elimination diet

There is more information on these tests below.

For a skin-prick test, the doctor puts drops of standardised food extracts on your arm. Then the skin is pricked with a small lancet, so the allergen can reach the cells of your immune system.

Sometimes the doctor does the test with a sample of the actual food thought to cause the reaction.

Itching, redness and swelling usually mean a positive reaction. The test is usually painless.

A skin-prick test does carry a small theoretical chance of causing anaphylaxis, but it is carried out where there are facilities to deal with this, usually an allergy clinic or a hospital, or a larger doctor's clinic.

If you'd rather not have a skin-prick test for a food allergy, a blood test is another option. It measures the amount of allergic antibodies in your blood.

In a food elimination diet, you stop eating the food thought to have caused the allergic reaction for two to six weeks. After that, the food is brought back into your diet.

If your symptoms go away while you avoid the food but return once you start eating it again, this normally points to a food allergy or intolerance.

Before you begin, you should get advice from a dietitian on things such as:

• the food and drinks you need to avoid
• how you should read and understand food labels
• whether you need any other sources of nutrition
• how long the diet should last

Don't try a food elimination diet on your own. Talk it over with a qualified health professional first.

Some tests sold in shops claim to detect allergies, but you should avoid them. They include:

• vega testing, which claims to detect allergies by measuring changes in your electromagnetic field
• kinesiology testing, which claims to detect food allergies by studying your muscle responses
• hair analysis, which claims to detect food allergies by taking a sample of your hair and running a series of tests on it
• alternative blood tests (leukocytotoxic tests), which claim to detect food allergies by checking for the "swelling of white blood cells"

Many of these testing kits are expensive. The scientific principles they are supposedly based on are unproven, and independent reviews have found them to be unreliable. So you should avoid them.

This advice is mainly written for parents of a child with a food allergy. But most of it applies to you too if you're an adult living with a food allergy.

There's no cure for food allergy at the moment, although many children grow out of certain ones, such as allergies to milk and eggs.

The most effective way to prevent symptoms is to take the food that causes the reaction (the allergen) out of your child's diet. But check with your doctor, or the doctor in charge of your child's care, before you cut out any food.

Taking eggs or peanuts out of a child's diet won't make much difference to their nutrition. Both are a good source of protein, and other foods can replace that protein.

A milk allergy can have more of an effect, because milk is a good source of calcium. There are still many other ways to get calcium into your child's diet, including green leafy vegetables. Many foods and drinks are also fortified with extra calcium.

See your doctor if you're worried that your child's allergy is affecting their growth and development.

Check the label of any pre-packed food or drink your child has, in case it contains something they're allergic to.

Under EU law, any pre-packed food or drink sold in the UK must clearly state on the label if it contains any of these ingredients:

• celery
• cereals that contain gluten, including wheat, rye, barley and oats
• crustaceans, including prawns, crabs and lobsters
• eggs
• fish
• lupin (common garden plants), and seeds from some varieties are sometimes used to make flour
• milk
• molluscs, including mussels and oysters
• mustard
• tree nuts, such as almonds, hazelnuts, walnuts, brazil nuts, cashews, pecans, pistachios and macadamia nuts
• peanuts
• sesame seeds
• soybeans
• sulphur dioxide and sulphites (preservatives used in some foods and drinks), at levels above 10mg per kg or per litre

Some food manufacturers also choose to add an allergy advice warning, for example "contains nuts", on pre-packed foods that hold an ingredient known to commonly cause an allergic reaction, such as peanuts, wheat, eggs or milk.

These warnings aren't compulsory, though. If a product has no allergy advice box or "contains" statement, it could still have any of the 14 specified allergens in it.

Look out for "may contain" labels, such as "may contain traces of peanut". Manufacturers sometimes use this to warn that a product may have become contaminated with another food while it was being made.

The UK Food Standards Agency website has more detailed information about allergen labelling.

Some non-food products contain allergy-causing food:

• some soaps and shampoos contain soy, egg and tree nut oil
• some pet foods contain milk and peanuts
• some glues and adhesive labels used on envelopes and stamps contain traces of wheat

So read the labels of any non-food products your child may come into close physical contact with.

Unpackaged food doesn't currently need to be labelled the same way as packaged food. This can make it harder to know what ingredients are in a particular dish.

Examples of unpackaged food include food sold from:

• bakeries, including in-store bakeries in supermarkets
• delis
• salad bars
• "ready-to-eat" sandwich shops
• takeaways
• restaurants

If you or your child have a severe food allergy, you need to be careful when you eat out.

The following advice should help:

• let the staff know: when booking a table at a restaurant, make sure the staff know about any allergies. Ask for a firm guarantee that the specific food won't be in any of the dishes served. The Food Standards Agency (FSA) offers chef cards that give information about allergies, and you can hand these to restaurant staff. Tell the chef and the kitchen staff who cook your food, and tell the waiters and waitresses too, so they understand why cross-contamination must be avoided when they serve you.
• read the menu carefully and check for hidden ingredients: some foods contain other foods that can trigger allergies, and restaurant staff may have overlooked this. Some desserts contain nuts (a cheesecake base, for example) and some sauces contain wheat and peanuts.
• prepare for the worst: it's a good idea to be ready for any eventuality. Always take anti-allergy medicine with you when you eat out, particularly an adrenalin auto-injector. Read more about treating food allergies with an auto-injector.
• use what's known as a taste test in older children: before your child begins to eat, ask them to take a tiny portion of the food and rub it against their lips, to see if they feel a tingling or burning sensation. If they do, it suggests the food will cause an allergic reaction. But the taste test doesn't work for all foods, so don't use it as a substitute for the advice above.

Here's some more advice for parents of a child with a food allergy:

• tell your child's school about the allergy. Depending on how severe it is, you may need to give the school staff an emergency action plan in case your child eats the food by accident. Ask the school nurse or another staff member to keep a supply of adrenalin. Food allergy bracelets are also available, and they explain how other people can help your child in an emergency.
• let other parents know. Young children can easily forget about their food allergy and accept food they shouldn't have when they visit other children. If you tell the parents of your child's friends about the allergy, it should help prevent this.
• teach your child. Once your child is old enough to understand the allergy, give them clear, simple instructions about which foods to avoid and what to do if they eat one of them by accident.

Two main types of medicine can relieve the symptoms of an allergic reaction to food:

• antihistamines, which are used to treat a mild to moderate allergic reaction
• adrenaline, which is used to treat a severe allergic reaction (anaphylaxis)

Antihistamines work by blocking histamine, the substance in your body that causes many of the symptoms of an allergic reaction.

You can buy many antihistamines from a pharmacy without a prescription, so it's sensible to keep a stock at home in case of an emergency. Non-drowsy antihistamines are preferred.

Some antihistamines, such as alimemazine and promethazine, aren't suitable for children under the age of two. If your child is younger than that and has a food allergy, ask your doctor which antihistamines may be suitable.

Don't drink alcohol after taking an antihistamine. It can make you feel drowsy and affect your ability to drive.

Adrenaline narrows the blood vessels, which works against the drop in blood pressure, and it opens up the airways so breathing becomes easier.

If you or your child is at risk of anaphylaxis, or has had an episode of anaphylaxis before, you'll be given an adrenaline auto-injector to use in an emergency.

Read the manufacturer's instructions that come with the auto-injector carefully. When your child is old enough, train them to use it too.

If you think someone is having an anaphylaxis reaction, call 999 and ask for an ambulance. Tell the operator you believe the person has anaphylaxis.

Older children and adults will probably have been trained to inject themselves. You may need to do it for a younger child, or for an older child or adult who is too sick to do it themselves.

There are three types of auto-injector:

• EpiPen
• Jext
• Emerade

All three work in much the same way. If anaphylaxis is suspected, take the safety cap off the injector and press it firmly against the thigh, holding it at a right angle. Don't use your thumb on the end of the injector.

You'll hear a "click" when the auto-injector has been activated. Keep it held in place for 10 seconds. Make sure you know the device well and which end goes against the thigh.

The injection can be given through clothing. A needle goes into the thigh and delivers a dose of adrenaline.

If the person is unconscious, check that their airways are open and clear, and check their breathing. Then put them in the recovery position. This stops an unconscious person from choking on their vomit.

Place the person on their side, 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.

As a precaution with a food allergy, you should follow this advice:

• Carry the auto-injector at all times, or encourage your child to do so if they're old enough. You may be prescribed two injectors, so check with your doctor 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 the contact details of their doctor, to alert others. Your child should wear this at all times.
• Extreme temperatures can make adrenaline less effective. Don't leave an auto-injector in places like your fridge or the glove compartment of your car.
• Check the expiry date regularly. 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 medicine for more information.
• If your child has an auto-injector, they'll 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.
• Don't delay injecting if you think you or your child may be experiencing the start of anaphylaxis, even if the first symptoms are mild. It's better to use adrenaline early and find out it was a false alarm than to delay treatment until you're sure your child is having severe anaphylaxis.

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