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
Food allergies are common, but they are not as widespread as many people think.
A number of surveys have found that 20-30% of 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 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.
Symptoms
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 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.
Causes
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 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.
Diagnosis
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.
Treatment
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.
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.
Eating out
If 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. 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 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).
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:
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 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.
The adrenaline inside the pen can go out of date, so check the date information on the label and replace it when necessary.
Prevention
Preventing food allergies in children
In the past, the Department of Health (DH) recommended that pregnant women whose children have a family history of allergic diseases avoided eating peanuts during pregnancy. This was thought to reduce the risk of their child developing a peanut allergy.
This advice was withdrawn in 2009 following a review of all the evidence that has become available in this area since the previous advice was issued in 1998. This review concluded that there is now no clear evidence that eating or not eating peanuts during pregnancy or while breastfeeding has an effect on the likelihood of a child developing a food allergy. For more information, read the Food Standards Agency advice on eating peanuts in pregnancy
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.
Government 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 and by going to Health A-Z: weaning babies
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 the UK 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 the trading standards service at your local authority.
