A food allergy is when the immune system experiences an adverse reaction to specific proteins found in food. It can cause serious illness
Introduction
Symptoms of a food allergy
Causes of a food allergy
Diagnosing food allergy
Treating a food allergy
Preventing a food allergy
See also: Allergies – Environmental
Introduction
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 90% of all food allergies.
In children, the foods that can cause an allergic reaction are:
- eggs,
- milk,
- soya,
- wheat, and
- peanuts.
In adults, the foods that can cause an allergic reaction are:
- crustaceans (shellfish), such as crab, lobster and prawns,
- tree nuts, such as walnuts, brazil nuts, almonds and pistachios,
- peanuts, and
- fish.
How common are food allergies?
Food allergies are common, but they are not as widespread as many people think.
A number of surveys have found that 1 in 5 people claim to have a food allergy. However, a Food Standards Agency (FSA) report in 2008 estimated that only 5-8% of children and 1-2% of adults have a food allergy. Some researchers believe that the figure for adults may be slightly higher, at around 3-4%.
The reason why many people may claim to 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.
A common misconception
Another widely held misconception is that deaths resulting from food allergies are widespread. This is possibly due to the fact that, when these types of deaths occur, they receive a lot of media coverage.
However, deaths from food allergies are very rare. In Englandin 2008, six deaths as a result of food allergies were recorded, which means that the chances of dying due to a food allergy in any given year is estimated to be 1 in 340,000.
Outlook
Most children will ‘outgrow’ food allergies to milk, eggs, soya and wheat by the time that 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 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.
Symptoms of a food allergy
The symptoms of a food allergy usually develop within a few minutes to an hour after exposure to the food.
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.
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 betweenthree and sixhours 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 immediatelyand ask foran ambulance if you think that you or someone you know is experiencing anaphylaxis.
Causes of a food allergy
The cause of food allergies is related to your immune system. 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
Food allergies, particularly peanut allergies, seem to run in families. If you have a parent, brother or sister with a peanut allergy, you are seven times more likely to develop a peanut allergy than someone with no family history of the condition.
This suggests that some food allergies, particularly peanut allergies, may be caused by specific genes that you inherit from your parents.
Other allergic conditions
Children who are born with 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 casesin 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 hypothesishas 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.
Diagnosing food allergy
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 of 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.
Treating a food allergy
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 the UK 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.
Many (but not all) pre-packed foods contain allergy advice warning labels if they contain a food that is known to commonly cause an allergic reaction, such as peanuts, eggs or milk.
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. If you are severely allergic to a particular food type, avoid these foods because there is no guarantee that they will be safe.
Some non-food products contain traces of allergy-causing food. For example:
- some soaps and shampoos contain traces of soy, egg and tree nut oil,
- some pet foods contain traces of milk and peanuts, and
- 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
Unpackaged food does not need to be labelled in the same way as packaged food, so there is a higher risk of accidental exposure, usually from cross-contamination.
Examples of unpackaged food include food sold from:
- bakeries,
- delis,
- salad bars,
- ‘ready-to-eat’ sandwich shops,
- take-aways, and
- restaurants.
If you have a severe food allergy, you may want to avoid eating unpackaged food.
Eating out
If your food allergy is not severe, there is no reason why you cannot visit restaurants as long as you 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 allergy-free. If the staff cannot offer such a guarantee, choose another restaurant. The Food Standards Agency (FSA) offers chef cards that provide information about your food allergy, which you can give to restaurant staff. 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 traces of other foods that can trigger allergies and which restaurant staff may have overlooked. For example, some desserts contain traces of nuts, some sauces contain traces of wheat and peanuts and some crisps contain traces of milk.
- 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’sschool 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:
- antihistamine tablets and/or gels, 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 will usually be given a device called anadrenaline 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.
There are two auto-injector pens available:
The adrenaline inside the pen can go out of date, so check the date information on the label and replace it when necessary.
Preventing a food allergy
Preventing food allergies in children
In the past, the Department of Health (DH) recommended that pregnant women with allergic conditions, or a history of allergies in their family, avoided eating peanuts during pregnancy. This was thought to reduce the risk of them giving birth to a child with a food allergy.
This advice was withdrawn in 2009 because there is little evidence that anything you eat during pregnancy, including peanuts, has an affect on the likelihood of your child developing a food allergy.
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, and
- to follow the Department of Health’s recommendations about breast feeding (children who are breastfed appear to have a lower risk of developing an allergic condition).
The Department of Health recommends that solid food should not be introduced before a baby is six months of age. It also recommends that, after six months, you should continue breas feeding and/or giving your baby breast milk substitute alongside solid food for up to two years of age or beyond.
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.