Allergy, food

A food allergy is when the immune system generates an adverse reaction to specific proteins found in food.

Symptoms of a food allergy can range from moderate, such as tingling in the mouth and a skin rash, to life threatening, such as a severe swelling of the throat that makes it difficult to breathe. A life-threatening allergic reaction is known as anaphylaxis.

Food types

Any food can potentially cause an allergic reaction, but there are eight types of foods that are responsible for the majority of all food allergies.

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

  • eggs
  • milk
  • soya
  • wheat
  • peanuts

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

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

How common are food allergies?

Food allergies are common, but they are not as widespread as many people think.

The reason why many people think they have a food allergy is that they mistake an intolerance to certain types of food (which does not involve the immune system) for a food allergy (which does).

For reasons that are not fully understood, rates of food allergy cases (but not deaths, see below) have risen sharply over the last two decades. See Causes for more information.

Outlook

Most children will 'outgrow' food allergies to milk, eggs, soya and wheat by the time that they start school.

Peanut allergies are usually more persistent. An estimated 80% of children with peanut allergies remain allergic to peanuts for the rest of their life.

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

There is currently no cure for food allergies. Treatment involves identifying the specific food that triggers the allergic reaction and then avoiding it.

If accidental exposure to an allergy-causing food occurs, anti-allergy medications can be used to relieve the symptoms. In cases of mild to moderate allergic reactions, medications such as antihistamines (which block the effects of a protein called histamine) can be used.

In the case of a severe anaphylactic reaction, an injection of a medication called adrenaline is required. As a precaution, people who have previously experienced an episode of anaphylaxis are often given an adrenaline injection device to carry with them.



Food allergy or intolerance?

The major differences between a food allergy and a food intolerance are listed below.

  • An allergy produces specific symptoms, such as swelling of the lips, which usually develops within minutes of eating the food, while an intolerance produces more general symptoms, such as indigestion and bloating, that can develop several hours after eating.
  • Only a tiny particle of food is needed to trigger a food allergy, whereas you would usually need to eat a larger amount of food to trigger an intolerance.
  • The symptoms of a food allergy can be life threatening, whereas the symptoms of a food intolerance, unpleasant as they can be, are never immediately life threatening.

Common symptoms include:

  • a tingling or burning sensation in your lips and mouth,
  • swelling of your lips or face,
  • an itchy, blotchy skin rash,
  • wheezing,
  • nausea,
  • abdominal pains,
  • vomiting,
  • diarrhoea, and
  • streaming eyes or nose.

The symptoms of a food allergy usually develop within a few minutes to an hour after exposure to the food.

Anaphylaxis

The symptoms of a severe anaphylactic reaction usually develop within a few minutes to a hour after exposure. However, there have been some cases of delayed reactions occurring between three and six hours after exposure (these cases involved a rare food allergy to meat).

The onset of the symptoms of an anaphylactic reaction is sudden and the symptoms can rapidly worsen. Symptoms include:

  • an itchy sensation in your throat,
  • rapid swelling of your throat, mouth, lips and face,
  • an itchy, red skin rash that quickly spreads across your body,
  • streaming eyes and nose,
  • sneezing,
  • nausea,
  • vomiting,
  • rapid heart beat (tachycardia),
  • increasing breathing difficulties due to swelling and tightening of your neck,
  • a sudden intense feeling of apprehension and fear (this has been described as a 'sense of impending doom'),
  • a sharp and sudden drop in your blood pressure, which can make you feel light-headed and confused, and
  • unconsciousness.

Anaphylaxis is a medical emergency and, without prompt treatment, it can lead to coma and possibly death.

Dial 999 immediately and ask for an ambulance with a paramedic if you think that you or someone you know is experiencing anaphylaxis.

Milk allergy and intolerance

All food allergies involve reactions by your immune system to that food. Your immune system is your body's main defence system against infection.

The immune system

The immune system protects the body by producing specialised cells called antibodies. These are the 'hunter-killer' cells of the body.

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 food allergies, a type of antibody known as immunoglobulin E (IgE) mistakenly targets a certain protein found in food as a threat to your body. The next time you come into contact with that food, the IgE antibodies trigger the release of a number of chemicals, of which the most important is 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 swell,
  • affects the nerves in the skin, which can cause the skin to feel itchy, and
  • increases the amount of mucus produced in your nose lining, causing local itching and burning.

In most allergic reactions to food, 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 into your blood. This causes in the wide range of symptoms associated with anaphylaxis.

Possible risk factors

Exactly why the IgE antibodies mistakenly target harmless food proteins is uncertain. 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 disease, such as asthma, eczema or a food allergy, you are at 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 are born with or acquire other allergic conditions, such as asthma or atopic dermatitis (an allergic skin condition), are more likely to develop a food allergy.

The rise in food allergy cases

Another puzzling aspect of food allergies is that the number of cases has risen sharply over the past two decades. For example, the number of children admitted to hospital for food-related anaphylaxis has risen by 700% since 1990.

There are a number of theories about this sharp increase, which are outlined below.

Changes in diet

One suggestion is that dietary changes in the western world may be responsible for the dramatic increase in the number of food allergy cases.

Some experts think that the increase in food allergy cases may be due to a decrease in the consumption of animal fats, such as butter and lard, and a corresponding increase in the consumption of vegetable fats and oils, such as margarine. The implication is that vegetable fats and oil may stimulate the over-production of IgE antibodies.

Another diet-related theory is that the decrease in the consumption of fresh fruit and vegetables may be responsible for the increase in food allergies.

These types of foods contain antioxidants, which are substances that help protect against cell damage. It is possible that a lack of antioxidants during early childhood may interfere with the normal development of the immune system in some children.

A third theory is that a reduction in Vitamin D in the diet may be responsible for the increase in food allergies. Vitamin D is found in oily fish, beef, cheese and eggs. It can also be produced naturally through the effects of sunlight on the skin.

Rates of food allergies are higher in countries that are nearer the North Pole, which may be due to a reduced exposure to sunlight.

Currently, there is no hard evidence to support (or disprove) any of these theories.

The hygiene hypothesis

Another theory for the significant increase in the number of food allergy cases in recent years is that children are increasingly growing up in 'germ-free' environments. This means that their immune system may not receive sufficient early exposure to the germs that it needs to develop properly.

This is known as the hygiene hypothesis. This hypothesis has also been suggested as the reason for the rise in other allergic conditions, such as asthma. However, as with the diet-related theories, there is little hard evidence to support or disprove the hygiene hypothesis in relation to food allergies.

Allergy to cows' milk is the most common food allergy in childhood, affecting 2-7% of babies aged under one.

Infant and follow-on formulas based on goats' milk protein are not suitable alternatives for infants intolerant or allergic to cows' milk. The proteins in cows' milk are similar to those found in other mammalian milks (such as sheep and goats) and someone allergic to cows' milk is likely to also be allergic to these other milks. Goats' milk formulas have not been approved for use in Europe.

Children usually grow out of milk allergy by the age of three, but about a fifth of these children will still have the allergy as adults.

Symptoms of milk allergy include rashes, diarrhoea, vomiting, stomach cramps and difficulty breathing.

Symptoms of a milk intolerance can include eczema, vomiting and diarrhoea (but not breathing problems). Children with a milk intolerance often grow out of it by school age.

See diagnosing food allergy

Foods that commonly cause allergy

  • Celeryor celeriac - this can sometimes cause anaphylactic shock
  • Wheat (all varieties, including spelt)
  • Gluten (see Health A-Z: coeliac disease for more information)
  • Egg - more common in childhood; about half of infants with an egg allergy will grow out of it by the age of three
  • Fish - raw and/or cooked fish can cause anaphylaxis in some people
  • Milk - babies and young children can be allergic or intolerant to milk (see Box, left)
  • Mustard
  • Nuts
  • Peanuts (these are actually legumes)
  • Sesame seeds
  • Shellfish
  • Soya - a common allergy in childhood; children usually grow out of it by the age of two
  • Quorn
  • Coconut
  • Fruit/vegetables - usually only cause mild reactions affecting the mouth
  • Kiwi fruit - the number of people allergic to this appears to be increasing
  • Pine nuts (a type of seed)
  • Meat - some people are allergic to just one type, while others are allergic to a range of meats; a common symptom is dermatitis (a skin reaction)

Visit your GP if you think you or your child has a food allergy.

Your GP will ask you questions about your or your child's suspected reaction to find out whether a food allergy is likely. Give them as much information as possible, including:

  • the type of symptoms you experience,
  • how long it takes for symptoms to develop after eating the food that caused the reaction, and
  • the type of food that caused the reaction, whether it was raw or cooked, and whether you were eating it at home or elsewhere, such as at a restaurant or picnic.

Your GP will also want to know whether there are symptoms of other allergies, such as asthma or hay fever, or whether these allergies are common in your family.

If your GP suspects that you or your child has a food allergy, you may be referred to an allergy clinic or centre for testing.

Skin prick testing

In a skin prick test, drops of diluted foods are placed on the arm. The skin is then pierced, through the drop, using a small needle or lancet (a double-edged tool that is similar to a scalpel) to introduce the food drops to the system. Itching, redness and swelling indicate a positive reaction. The test is very safe for people of all ages.

However, while a skin prick test is a useful screening tool, it is not 100% reliable. The test can sometimes wrongly give a positive result for an allergy when no allergy exists (a false positive result), or it can give a negative result when you do have an allergy (a false negative result).

Therefore, further testing is usually recommended to confirm or disprove the results of your skin prick test.

Blood tests

Blood tests for food allergies involve exposing you to a small sample of suspected foods and then checking your blood to see whether the food has led to an increase in specific IgE antibodies.

As with the skin prick test, blood tests are not 100% reliable because they can often give a high number of false negative results.

Exclusion diets and food diaries

An exclusion diet is where you remove certain types of food from your diet to see whether your symptoms improve, then reintroduce the food to see if it leads to a recurrence of your symptoms.

It is recommended that you only carry out an exclusion diet under the supervision of a dietitian or other qualified healthcare professional. Cutting out entire classes of food, such as dairy products or wheat, without proper supervision can be potentially dangerous, particularly in children.

In combination with the exclusion diet, you may also be asked to keep a food diary, in which you record the different types of food that you eat to observe the effect they have on your symptoms.

Blinded challenge testing

Blinded challenge testing is regarded as the gold standard test for food allergies. Gold standard means that it is the most accurate form of testing that is currently available.

During the test, you will be given a number of different foods, one of which will have a small sample of the suspected foodstuff hidden inside it. You will then be asked to eat each type of food to see how you react.

The reasons that the test is blinded and the food is hidden is that a small amount of people experience a psychological reaction to foods that they suspect are causing their allergies, which can distort the test results.

Never attempt to carry out a challenge test at home because there is a small risk that you will have an anaphylactic reaction.

Blind challenge testing should only be carried out at a suitable medical facility under the supervision of staff who are experienced in treating anaphylaxis.

Useful Links

The Food Safety Authority of Ireland (FSAI) today announced that it is providing a new free email and SMS text service which will directly inform food allergy sufferers of the presence of allergens in inappropriately labelled foods.

Useful Links

Alternative testing kits

There are a number of shop-bought tests available which claim to detect allergies. They include:

  • Vega testing, which claims to be able to detect food allergies by measuring changes in your electromagnetic field.
  • Kinesiology testing, which claims to be able to detect food allergies by studying your muscle responses.
  • Hair analysis, which claims to be able 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 alternative testing kits are expensive, the scientific principles they are alleged to be based on are unproven and, in independent tests, all have been found to be completely unreliable. They should, therefore, be avoided.

Once you have been diagnosed as having a food allergy, your treatment will involve two important elements:

  • providing you with information and advice about the best way to avoid coming into contact with the offending foodstuff (often referred to as an elimination diet), and
  • drawing up an emergency care plan that you can use if you accidentally come into contact with the offending food.

Elimination diet

Depending on the type of food that you are allergic to, you may be referred to a dietitian. This is in case eliminating that food from your diet would have an adverse impact on your nutrition.

For example, an allergy to peanuts is unlikely to affect your diet, but an allergy to milk may mean that you will need to find alternative sources of calcium.

It is important that, as part of your elimination diet, you avoid all contact with the offending food. Therefore, as well as avoid eating or drinking the food, you will also need to avoid:

  • inhaling the food, for example accidentally sniffing some peanut dust,
  • touching the food, and
  • cross-contamination.

Cross-contamination is when utensils, such as knives and forks or work surfaces, such as chopping boards, become contaminated with the offending food through shared use.

Reading labels

As part of your elimination diet, it is very important that you read the list of ingredients on the label of any pre-packed food or drink products you buy.

Under European Union law, any pre-packed food or drink that is sold in Ireland must clearly state on the label if it contains the following ingredients:

  • celery,
  • cereals that contain gluten (including wheat, rye, barley and oats),
  • crustaceans (including prawns, crabs and lobsters),
  • eggs,
  • fish,
  • lupin (lupins are common garden plants and the 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, and
  • sulphur dioxide and sulphites (preservatives that are used in some foods and drinks) at levels above 10mg per kg or per litre.

Some food manufacturers also choose to put allergy advice warning labels ('contains xxx') on their pre-packed foods if they contain an ingredient that is known to commonly cause an allergic reaction, such as peanuts, eggs or milk. However, these are not compulsory. If there is no allergy advice box or 'contains' statement on a product, it does not mean that none of the 14 specified allergens are used as ingredients.

Look out for 'may contain' labels, such as 'may contain traces of peanut'. Manufacturers sometimes put this label on their products to warn consumers that they may have become contaminated with another food product during the manufacturing process.

Some non-food products contain allergy-causing food. For example:

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

Again, read the labels of any non-food products that you may come into close physical contact with.

Unpackaged food

Currently, unpackaged food does not need to be labelled in the same way as packaged food, and therefore it can be more difficult for the food allergic consumer to know what ingredients are used 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,
  • take-aways, and
  • restaurants.

If you have a severe food allergy, you will need to be careful if you want to eat out.

f you wish to eat unpackaged foods, you should follow the advice below.

  • Let the staff know. When making a booking at a restaurant, make sure that the staff are aware of your allergy and ask for a firm guarantee that any food you will be served will be free from the food to which you are allergic. If the staff cannot offer such a guarantee, choose another restaurant. As well as informing the chef and kitchen staff who are involved in cooking your food, let waiters and waitresses know so that they understand the importance of avoiding cross-contamination when serving you.
  • Read the menu carefully and check for 'hidden ingredients'. Some food types contain other foods that can trigger allergies and which restaurant staff may have overlooked. For example, some desserts contain nuts (e.g. in a cheesecake base), and some sauces contain wheat and peanuts.
  • Use the 'taste-test'. Before you begin to eat, take a tiny portion of the food and rub it against your lips to see if you experience a tingling or burning sensation. If you do, it suggests that the food will cause you to have an allergic reaction. However, the 'taste-test' does not always work for all foods, so it should not be used as a substitute for not following the advice above.
  • Prepare for the worst. If you follow the advice outlined above, you should not experience any problems, although it is also a good idea to prepare for any eventuality. Always take your anti-allergy medication with you when eating out, particularly if you have been given an auto-injector of adrenalin (see below).

Children

The above advice regarding diet also applies to children with a food allergy. There is some additional advice that you should follow if your child has a food allergy.

  • Notify your child's school about their allergy. Depending how severe your child's allergy could be, it may be useful to provide the staff at their school with an emergency action plan in case of accidental exposure. Arrange with the school nurse, or another appropriate staff member, to hold a supply of adrenalin and to administer it if necessary. Food allergy bracelets are also available, which explain how other people can help your child in an emergency.
  • Let other parents know. Young children may easily forget about their food allergy and accept food that they should not have when visiting other children. Telling the parents of your child's friends about their allergy should help prevent this.
  • Educate your child. Once your child is old enough to understand, it is important that you provide them with clear, simple instructions about what foods to avoid and what they should do in the case of accidental exposure.

Emergency care plan

As part of your emergency care plan, you will usually be given two types of medication that you should keep with you at all times:

  • antihistamines, which can be used to manage the symptoms of a mild to moderate allergic reaction, and
  • adrenaline, which is used to manage the symptoms of anaphylaxis.

Antihistamines work by blocking the effects of histamine, a protein responsible for most of the symptoms of an allergic reaction.

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

You may be advised to have a device called an adrenaline auto-injector pen. This looks similar to a felt-tip pen and consists of a syringe and a pre-packaged dose of adrenaline.

If you think that you are experiencing an anaphylactic reaction, inject yourself in your thigh or upper arm with the pen before dialling 999 and asking for an ambulance with a paramedic.

There are two auto-injector pens available:

  • EpiPen
  • Anapen

The adrenaline inside the pen can go out of date, so check the date information on the label and replace it when necessary.

A balanced diet

It is strongly recommended that you do not go on a strict diet involving very few foods to self-diagnose or treat food allergies without seeking medical advice.

Preventing food allergies in children

From the limited evidence that is available, the most effective way of reducing your child's risk of developing a food allergy is to avoid smoking during pregnancy and to make sure that your baby is not exposed to second-hand smoke.

HSE advice to all mothers is to try to exclusively breastfeed their baby until around six months of age. Solid foods should be introduced when an infant is around six months old, alongside continued breastfeeding. If mothers choose to start giving their babies solid food before six months of age, they should avoid giving the commonly allergenic foods (milk, egg, peanuts, nuts, fish, wheat). If a baby already has a diagnosed allergic disease such as eczema or a food allergy, they could be at higher risk of developing peanut allergy. The mothers of these children should talk to their health professional before giving peanuts to their child for the first time.

More advice on feeding infants is available from health professionals

When introducing solid foods that are known to be linked to allergies, such as nuts or eggs, introduce them one at a time so that you can spot any potential allergic reaction (see Food allergy - Symptoms).

Buying food

Make sure you look carefully at the label on any pre-packed food you buy if you have a food allergy or intolerance, or if you are buying food for someone who does. Check the ingredients, then check for any allergy statements or boxes.

Every pre-packed food and drink sold in Ireland or the rest of the European Union (EU) must show clearly on the label if it contains one of the following:

  • celery
  • cereals containing gluten (including wheat, rye, barley and oats)
  • crustaceans (including prawns, crabs and lobsters)
  • eggs
  • fish
  • lupin
  • milk
  • molluscs (including mussels and oysters)
  • mustard
  • 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

'May contain' labelling

Some food labels say 'may contain nuts' or 'may contain seeds'. This means that even though nuts or seeds are not deliberately included in the food, the manufacturer cannot be sure that the product does not accidentally contain small amounts of them. If you have a nut or seed allergy, you should avoid these food products.

If you think a food product has been labelled incorrectly, report this to your local HSE Environmental Health Office.

There is a danger when you have a food allergy that you will come to view many foods suspiciously or that you avoid eating properly through fear. Discuss these concerns with your doctor and dietitian so they can ensure you eat a balanced diet, with all the essential elements.

It's important to moderate alcohol intake if you're severely allergic because alcohol can dull your senses and slow your response to accidental exposure to a culprit food. You are also more likely to let your guard slip when under the influence of alcohol and risk eating something that may not be safe. For the same reasons, and many others, avoid all recreational drug use.

Stress hampers the healthy working of the immune system, so keep your stress levels down. You can achieve this through regular exercise or relaxation therapies, such as meditation, aromatherapy or yoga.

Talking to someone who is going through the same thing as you can be extremely beneficial. The allergy charities have helplines that you can call if you want to discuss anything concerning your food allergy and wider health, and there are many online allergy forums which can connect you with other people with food allergies.

Although it is beneficial to your health to give up smoking, there is no known connection between smoking and allergic reactions to food.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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