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About food allergies
A food allergy is when the body's immune system reacts unusually to specific foods. Although allergic reactions are often mild, they can be very serious.
Symptoms of a food allergy can affect different areas of the body at the same time. Some common symptoms include:
- an itchy sensation inside the mouth, throat or ears
- a raised itchy red rash (urticaria, or "hives")
- swelling of the face, around the eyes, lips, tongue and roof of the mouth (angioedema)
Read more about the symptoms of food allergies
In the most serious cases, a person has a severe allergic reaction (anaphylaxis), which can be life threatening.
If you think someone has the symptoms of anaphylaxis – such as breathing difficulties, lightheadedness, and feeling like they're going to faint or lose consciousness – call 999.
Ask for an ambulance and tell the operator you think the person has anaphylaxis or "anaphylactic shock".
What causes food allergies?
Food allergies happen when the immune system – the body's defence against infection – mistakenly treats proteins found in food as a threat.
As a result, a number of chemicals are released. It's these chemicals that cause the symptoms of an allergic reaction.
Almost any food can cause an allergic reaction, but there are certain foods that are responsible for most food allergies.
In children, the foods that most commonly cause an allergic reaction are:
- tree nuts
Most children that have a food allergy will have experienced eczema during infancy. The worse the child's eczema and the earlier it started, the more likely they are to have a food allergy.
In adults, the foods that most commonly cause an allergic reaction are:
- tree nuts – such as walnuts, brazil nuts, almonds and hazelnuts
- fruits – such as apples and peaches
- 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.
Read more information about the causes and risk factors for food allergies
Types of food allergies
Food allergies are divided into three types, depending on symptoms and when they occur.
- IgE-mediated food allergy – the most common type, triggered by the immune system producing an antibody called immunoglobulin E (IgE). Symptoms occur a few seconds or minutes after eating. There's a greater risk of anaphylaxis with this type of allergy.
- non-IgE-mediated food allergy – these allergic reactions aren't caused by immunoglobulin E, but by other cells in the immune system. This type of allergy is often difficult to diagnose as symptoms take much longer to develop (up to several hours).
- mixed IgE and non-IgE-mediated food allergies – some people may experience symptoms from both types.
Read more information about the symptoms of a food allergy
Oral allergy syndrome (pollen-food syndrome)
Some people experience itchiness in their mouth and throat, sometimes with mild swelling, immediately after eating fresh fruit or vegetables. This is known as oral allergy syndrome.
Oral allergy syndrome is caused by allergy antibodies mistaking certain proteins in fresh fruits, nuts or vegetables for pollen.
Oral allergy syndrome generally doesn't cause severe symptoms, and it's possible to deactivate the allergens by thoroughly cooking any fruit and vegetables.
Some people with pollen-food syndrome may have more severe symptoms.
The Allergy UK website has more information on oral allergy syndrome.
The best way of preventing an allergic reaction is to identify the food that causes the allergy and avoid it.
Research is currently looking at ways to desensitise some food allergens, such as peanuts and milk, but this is not an established treatment.
Read more about identifying foods that cause allergies (allergens)
Avoid making any radical changes, such as cutting out dairy products, to your or your child's diet without first talking to your GP. For some foods, such as milk, you may need to speak to a dietitian before making any changes.
A type of medication called an antihistamine can help relieve the symptoms of a mild or moderate allergic reaction. A higher dose of 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 known as an auto-injector pen, which contains doses of adrenaline that can be used in emergencies.
Read more about the treatment of food allergies
When to seek medical advice
If you think you or your child may have a food allergy, it's very important to ask for a professional diagnosis from your GP. They can then refer you to an allergy clinic if appropriate.
Many parents mistakenly assume their child has a food allergy when their symptoms are actually caused by a completely different condition.
Commercial allergy testing kits are available, but using them isn't recommended. Many kits are based on unsound scientific principles. Even if they're reliable, you should have the results looked at by a health professional.
Read more about diagnosing food allergies
Most food allergies affect younger children under the age of three. It's estimated around 1 in every 14 children of this age has at least one food allergy.
Most children who have food allergies to milk, eggs, soya and wheat in early life will grow out of it by the time they start school.
Peanut and tree nut allergies are usually more persistent. An estimated four out of five children with peanut allergies remain allergic to peanuts for the rest of their lives.
Food allergies that develop during adulthood, or persist into adulthood, are likely to be lifelong allergies.
For reasons that are unclear, rates of food allergies have risen sharply in the last 20 years.
However, deaths from anaphylaxis-related food reactions are now rare.
Symptoms of a food allergy
The symptoms of a food allergy almost always develop a few seconds or minutes after eating the food.
Some people may develop a severe allergic reaction (anaphylaxis), which can be life threatening.
The most common type of allergic reaction to food is known as an IgE-mediated food allergy.
- tingling or itching in the mouth
- a raised, itchy red rash (urticarial) – in some cases, the skin can turn 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)
The symptoms of a severe allergic reaction (anaphylaxis) can be sudden and get worse very quickly.
Initial symptoms of anaphylaxis are often the same as those listed above and can lead to:
- increased breathing difficulties – such as wheezing and a cough
- a sudden and intense feeling of anxiety and fear
- a rapid heartbeat (tachycardia)
- a sharp and sudden drop in your blood pressure, which can make you feel lightheaded and confused
Anaphylaxis is a medical emergency. Without quick treatment, it can be life threatening. If you think you or someone you know is experiencing anaphylaxis, dial 999 and ask for an ambulance as soon as possible.
Non-IgE-mediated food allergy
Another type of allergic reaction is a non-IgE-mediated food allergy. The symptoms of this type of allergy can take much longer to develop – sometimes up to several days.
Some symptoms of a non IgE-mediated food allergy may be what you would expect to see in an allergic reaction, such as:
- redness and itchiness of the skin – although not a raised, itchy red rash (urticarial)
- the skin becomes itchy, red, dry and cracked (atopic eczema)
Other symptoms can be much less obvious and are sometimes thought of as being caused by something other than an allergy. They include:
- heartburn and indigestion 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)
- redness around the anus, rectum and genitals
- unusually pale skin
- failure to grow at the expected rate
Some children can have a mixed reaction where they experience both IgE symptoms, such as swelling, and non-IgE symptoms, such as constipation.
This can happen to children who have a milk allergy.
Causes of a food allergy
A food allergy is caused by your immune system handling harmless proteins in certain foods as a threat. It releases a number of chemicals, which trigger an allergic reaction.
The immune system
The immune system protects the body by producing specialised proteins called antibodies.
Antibodies identify potential threats to your body, such as bacteria and viruses. They signal your immune system to release chemicals to kill the threat and prevent the spread of infection.
In the most common type of food allergy, an antibody known as immunoglobulin E (IgE) mistakenly targets a certain protein found in food as a threat. IgE can cause several chemicals to be released, the most important being histamine.
Histamine causes most of the typical symptoms that occur during an allergic reaction. For example, histamine:
- causes small blood vessels to expand and the surrounding skin to become red and swell up
- affects nerves in the skin, causing itchiness
- increases the amount of mucus produced in your nose lining, which causes itching and a burning sensation
In most food allergies, the release of histamine is limited to certain parts of the body, such as your mouth, throat or skin.
In anaphylaxis, the immune system goes into overdrive and releases massive amounts of histamine and many other chemicals into your blood. This causes the wide range of symptoms associated with anaphylaxis.
Non-IgE-mediated food allergy
There's another type of food allergy known as a non-IgE-mediated food allergy, caused by different cells in the immune system.
This is much harder to diagnose as there's no test to accurately confirm non-IgE-mediated food allergy.
This type of reaction is largely confined to the skin and digestive system, causing symptoms such as heartburn, indigestion and eczema.
In babies, a non-IgE-mediated food allergy can also cause diarrhoea and reflux, where stomach acid leaks up into the throat.
In children, the foods that most commonly cause an allergic reaction are:
- milk – if a child has an allergy to cow's milk, they're probably allergic to all types of milk, as well as infants' and follow-on formula
In adults, the foods that most commonly cause an allergic reaction are:
- tree nuts – such as walnuts, brazil nuts, almonds and pistachios
- 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
- sesame seeds
- fruit and vegetables – these usually only cause symptoms affecting the mouth, lips and throat (oral allergy syndrome)
- pine nuts (a type of seed)
- meat – some people are allergic to just one type of meat, while others are allergic to a range of meats; a common symptom is skin irritation
Who's at risk?
Exactly what causes the immune system to mistake harmless proteins as a threat is unclear. However, a number of risk factors for food allergies have been identified, which are outlined below.
If you have a parent, brother or sister with an allergic condition – such as asthma, eczema or a food allergy – you have a slightly higher risk of developing a food allergy. However, you may not develop the same food allergy as your family members.
Other allergic conditions
Children who have atopic dermatitis (eczema) in early life are more likely to develop a food allergy.
The rise in food allergy cases
The number of people with food allergies has risen sharply over the past few decades and, although the reason is unclear, other allergic conditions such as atopic dermatitis have also increased.
One theory behind the rise is that a typical child's diet has changed considerably over the last 30 to 40 years.
Another theory is that children are increasingly growing up in "germ-free" environments. This means their immune systems may not receive sufficient early exposure to the germs needed to develop properly. This is known as the hygiene hypothesis.
It's rare for someone to have an allergic reaction to food additives. However, certain additives may cause a flare-up of symptoms in people with pre-existing conditions.
Sulphur dioxide (E220) and other sulphites (E221, E222, E223, E224, E226, E227 and E228) are used as preservatives in a wide range of foods, especially soft drinks, sausages, burgers, and dried fruits and vegetables.
Sulphur dioxide is produced naturally when wine and beer are made, and is 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 require pre-packed food sold in the UK, and the rest of the European Union, to show clearly on the label if it contains sulphur dioxide or sulphites at levels above 10mg per kg or per litre.
Benzoic acid (E210) and other benzoates (E211, E212, E213, E214, E215, E218 and E219) are used as food preservatives to prevent yeasts and moulds growing, most commonly in soft drinks. They occur naturally in fruit and honey.
Benzoates could make the symptoms of asthma and eczema worse in children who already have these conditions.
Diagnosing food allergy
If you think you or your child has a food allergy, make an appointment with your GP.
They 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?
Your GP may also assess your child's weight and size to make sure they're growing at the expected rate.
Referral to an allergy clinic
If your GP suspects a food allergy, you may be referred to an allergy clinic or centre for testing.
The tests needed can vary, depending on the type of allergy:
- if the symptoms developed quickly (an IgE-mediated food allergy) – you'll probably be given a skin-prick test or a blood test
- if the symptoms developed more slowly (non-IgE-mediated food allergy) – you'll probably be put on a food elimination diet
There is more information on these tests below.
During a skin-prick test, drops of standardised extracts of foods are placed on the arm. The skin is then pierced with a small lancet, which allows the allergen to come into contact with the cells of your immune system.
Occasionally, your doctor may perform the test using a sample of the food thought to cause a reaction.
Itching, redness and swelling usually indicates a positive reaction. This test is usually painless.
A skin-prick test does have a small theoretical chance of causing anaphylaxis, but testing will be carried out where there are facilities to deal with this – usually an allergy clinic, hospital, or larger GP surgery.
An alternative to a skin-prick test is a blood test, which measures the amount of allergic antibodies in the blood.
Food elimination diet
In a food elimination diet, the food thought to have caused the allergic reaction is withdrawn from the diet for two to six weeks. The food is then reintroduced.
If the symptoms go away when the food is withdrawn but return once the food is introduced again, this normally suggests a food allergy or intolerance.
Before starting the diet, you should be given advice from a dietitian on issues such as:
- the food and drinks you need to avoid
- how you should interpret food labels
- if any alternative sources of nutrition are needed
- how long the diet should last
Don't attempt a food elimination diet by yourself without discussing it with a qualified health professional.
There are several shop-bought tests available that claim to detect allergies, but should be avoided.
- vega testing – claims to detect allergies by measuring changes in your electromagnetic field
- kinesiology testing – claims to detect food allergies by studying your muscle responses
- hair analysis – 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) – 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 allegedly based on are unproven, and independent reviews have found them to be unreliable. They should therefore be avoided.
Living with a food allergy
The advice here is primarily written for parents of a child with a food allergy. However, most of it is also relevant if you're an adult with a food allergy.
Your child's diet
There's currently no cure for food allergies, although many children will grow out of certain ones, such as allergies to milk and eggs.
The most effective way you can prevent symptoms is to remove the offending food – known as an allergen – from their diet.
However, it's important to check with your GP or the doctor in charge of your child's care first before eliminating certain foods.
Removing eggs or peanuts from a child's diet isn't going to have much of an impact on their nutrition. Both of these are a good source of protein, but can be replaced by other, alternative sources.
A milk allergy can have more of an impact as milk is a good source of calcium, but there are many other ways you can incorporate calcium into your child's diet, including green leafy vegetables. Many foods and drinks are fortified with extra calcium.
See your GP if you're concerned that your child's allergy is affecting their growth and development.
It's very important to check the label of any pre-packed food or drinks your child has in case it contains ingredients 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 the following ingredients:
- cereals that contain gluten – including wheat, rye, barley and oats
- crustaceans – including prawns, crabs and lobsters
- lupin (common garden plants) – seeds from some varieties are sometimes used to make flour
- molluscs – including mussels and oysters
- tree nuts – such as almonds, hazelnuts, walnuts, brazil nuts, cashews, pecans, pistachios and macadamia nuts
- sesame seeds
- 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 put allergy advice warning labels – for example, "contains nuts" – on their pre-packed foods if they contain an ingredient known to commonly cause an allergic reaction, such as peanuts, wheat, eggs or milk.
However, these aren't compulsory. If there's no allergy advice box or "contains" statement on a product, 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 put this label on their products to warn consumers that they may have become contaminated with another food product when being made.
Read more detailed information about allergen labelling on the Food Standards Agency website.
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
Again, read the labels of any non-food products your child may come into close physical contact with.
Currently, unpackaged food doesn't need to be labelled in the same way as packaged food. This can make it more difficult to know what ingredients are in a particular dish.
Examples of unpackaged food include food sold from:
- bakeries – including in-store bakeries in supermarkets
- salad bars
- "ready-to-eat" sandwich shops
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 provide information about allergies, which you can give to restaurant staff. As well as informing the chef and kitchen staff involved in cooking your food, let waiters and waitresses know so 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, which restaurant staff may have overlooked. Some desserts contain nuts (such as a cheesecake base) and some sauces contain wheat and peanuts.
- prepare for the worst – it's a good idea to prepare for any eventuality. Always take anti-allergy medication with you when eating out, particularly an adrenalin auto-injector. Read more about treating food allergies with a 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 experience a tingling or burning sensation. If they do, it suggests that the food will cause them to have an allergic reaction. However, the taste test doesn't work for all foods, so it shouldn't be used as a substitute for the above advice.
Here's some more advice for parents:
- notify your child's school about their allergy – depending on how severe their allergy is, it may be necessary to give the staff at their school an emergency action plan in case of accidental exposure. Arrange for the school nurse or another staff member to hold a supply of adrenalin. Food allergy bracelets, which explain how other people can help your child in an emergency, are also available.
- let other parents know – young children may easily forget about their food allergy and accept food they shouldn't 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 their allergy, it's important to give them clear, simple instructions about what foods to avoid and what they should do if they accidentally eat them.
Treating a food allergy
There are two main types of medication that can be used to relieve the symptoms of an allergic reaction to foods:
- antihistamines – used to treat mild to moderate allergic reaction
- adrenaline – used to treat severe allergic reactions (anaphylaxis)
Antihistamines work by blocking the effects of histamine, which is responsible for many of the symptoms of an allergic reaction.
Many antihistamines are available from your pharmacist without prescription – stock up in case of an emergency. Non-drowsy antihistamines are preferred.
Some antihistamines, such as alimemazine and promethazine, aren't suitable for children under the age of two.
If you have a younger child with a food allergy, ask your GP about what types of antihistamines may be suitable.
Avoid drinking alcohol after taking an antihistamine as this can make you feel drowsy and affect your ability to drive.
Adrenaline works by narrowing the blood vessels to counteract the effects of low blood pressure and opening up the airways to help ease breathing difficulties.
You'll be given an auto-injector of adrenaline to use in case of emergencies if you or your child is at risk of anaphylaxis or had a previous episode of anaphylaxis.
Read the manufacturer's instructions that come with the auto-injector carefully and train your child how to use it when they are old enough.
Using an auto-injector
If you suspect that somebody is experiencing the symptoms of anaphylaxis, call 999 and ask for an ambulance. Tell the operator that you think the person has anaphylaxis.
Older children and adults will probably have been trained to inject themselves. You may need to inject younger children or older children and adults who are too sick to inject themselves.
There are three types of auto-injectors:
All three work in much the same way. If anaphylaxis is suspected, you should remove the safety cap from the injector and press firmly against the thigh, holding it at a right angle, without using the thumb at the end.
A "click" indicates the auto-injector has been activated, and it should be held in place for 10 seconds. Ensure you're familiar with the device and know the correct end to place against the thigh.
The injections can be given through clothing. This will send a needle into your thigh and deliver a dose of adrenaline.
If the person is unconscious, check their airways are open and clear, and check their breathing. Then put them in the recovery position. Putting someone who is unconscious in the recovery position ensures they don't choke on their vomit.
Place the person on their side, making sure they're supported by one leg and one arm. Open the airway by tilting the head and lifting the chin.
If the person's breathing or heart stops, cardiopulmonary resuscitation (CPR) should be performed.
Owning an auto-injector
As a precaution, the following advice should be taken:
- Carry the auto-injector at all times or encourage your child to do so if they're old enough. You may be prescribed two injectors – check with your GP or the doctor in charge of your care. You may also be given an emergency card or bracelet with full details of your child's allergy and the contact details of their doctor to alert others. They 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 medication 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 initial symptoms are mild. It's better to use adrenaline early and find out it was a false alarm than delay treatment until you're sure your child is experiencing severe anaphylaxis.
10 March 2023
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