Food allergy
Your health expert: Dr
Iason Thomas, Consultant Allergist
Content editor review by Pippa Coulter, Freelance Health Editor, July 2023
Next review due July 2026
A food allergy is when your body’s immune system reacts to a certain food, such as eggs or nuts, as if they were harmful. This can affect your body in different ways. If your allergy is severe, the reaction can be life-threatening.
About food allergies
An allergy is when your immune system reacts to something that’s usually harmless. The triggers for the allergic response are called allergens. In most people, these allergens don’t cause any problems. But if you have an allergy, your immune system sees them as a ‘threat’ and overreacts. This causes the symptoms of an allergic reaction. Most food allergies happen when you eat some of the allergen. More rarely, just breathing in or having skin contact with the allergen is enough to set off an allergic reaction.
There are different types of allergic reaction. These include the following.
- An immediate allergic reaction, which can cause skin, stomach, circulation and breathing problems. This is caused by antibodies called immunoglobulin E (or IgE). The symptoms normally pass within 12 hours.
- A more gradual, delayed reaction, which can develop over a longer period of time. This is caused by cells in your immune system called T cells. It's most likely to just cause stomach problems.
- A mixture of both types.
Both children and adults can have food allergies, although children often grow out of them as they get older.
A food allergy is different from a food intolerance. Food allergy reactions involve your immune system, whereas a food intolerance doesn’t. Your body might not be able to break down certain foods as well if you have a food intolerance, or you might react to specific chemicals in foods. The symptoms of a food intolerance usually develop more slowly than with a food allergy.
Common food allergies
Lots of different foods can cause an allergic reaction. But the most common food allergies include the following.
- Cow’s milk. Children with cow’s milk allergy almost always develop it before the age of one. Most children grow out of it by the time they are adults. If you’re allergic to cow’s milk, you’re more likely to be allergic to goat’s and sheep’s milk too.
- Eggs. This also usually develops before the age of one. Most children will outgrow egg allergy, as they get older with many developing some tolerance by the age of five.
- Peanuts. This usually develops in childhood, but is less likely to go away than milk and egg allergies. It’s one of the most common causes of severe allergic reactions.
- Tree nuts, including hazelnuts, Brazil nuts, almonds, cashews and walnuts. If you’re allergic to peanuts, you may also have an allergy to tree nuts.
- Wheat. This mainly affects children, but it can sometimes trigger an allergic reaction in adults if they exercise soon after eating it.
- Fish and shellfish. Fish allergy is more common in children, and shellfish allergy in adults. People are often allergic to several different types of fish or shellfish.
- Raw fruits and vegetables. This can be part of a syndrome called Pollen Food Syndrome or Oral Allergy Syndrome, which is linked to allergy to tree or grass pollen. It most commonly involves apples and fruits with stones, such as peaches, plums and cherries. But almost any fruit, vegetables or nuts can trigger a reaction. It tends to cause a mild allergic reaction in your mouth.
- Soy. This usually starts in babies or children. Most children outgrow it as they get older. Occasionally it can start in teenagers or adults if they have developed Pollen Food Syndrome.
- Sesame seeds. This usually develops before the age of two, and most people continue to be allergic as adults.
Causes of food allergy
It’s unclear exactly why some people develop a food allergy, but it’s thought likely to be due to a combination of factors. The following things are known to increase your risk.
- Having eczema or skin infections before the age of one.
- Having family members who have food allergies or other allergic conditions.
- Already having one food allergy tends to increase your risk of getting another one.
There’s some suggestions that not being exposed to many germs (bacteria) in your childhood may increase the risk. Children with more siblings or who attend childcare settings are less likely to have food allergies. This might be because they’re exposed to more germs.
Food allergy symptoms
For most food allergies, symptoms come on very quickly. This is usually within 20 minutes after you’ve eaten or been in contact with the food and almost always within two hours. Just eating a tiny amount of a food allergen, or even breathing it in or touching it may trigger a reaction. You may have some of the following symptoms.
- Itchy, red and swollen skin (often around your lips, face or eyes), and a rash
- Sore, red, swollen or itchy eyes
- Wheezing, a cough, noisy breathing or shortness of breath
- An itchy or tingling feeling and swelling in your mouth, including your lips and tongue.
- A runny, blocked or itchy nose and sneezing
- Diarrhoea, bloating or tummy cramps
- Feeling sick or vomiting
These symptoms don’t always mean you have a food allergy. But contact your GP if you do notice symptoms after eating certain foods.
Severe reactions
Food allergies can also cause a severe allergic reaction called anaphylaxis, which affects your whole body. You may have difficulties breathing and circulation problems. You might feel drowsy or pass out (lose consciousness). Anaphylaxis can be life-threatening and you’ll need medical help straightaway. If someone is having trouble breathing or is losing consciousness, call 999 immediately.
Diagnosis of food allergy
Your GP will ask you about your symptoms, including how often you’ve had them, how long they last and how severe they are. They’ll want to know what foods you ate before the reaction, how much you ate and how quickly your symptoms developed after eating them. It can be helpful to keep a food diary (PDF, 1.4MB) to keep track of this.
Your GP will also ask whether you have any allergy-related conditions, such as eczema or asthma. They’ll also want to know whether anyone in your family has food allergies.
Food allergy testing
If your GP thinks you have a food allergy, they may refer you to a doctor specialising in allergies. The specialist will be able to carry out food allergy tests to confirm what foods are causing your reaction. Common allergy tests are listed below.
- Skin prick tests. In this test, an extract from the food is put directly onto your skin, where your doctor makes a tiny prick. Your doctor examines your skin after about 15 minutes to see if you’ve had a reaction.
- Serum IgE test.This measures the amount of antibodies, called immunoglobulin E (IgE) in your blood. You might have this test if you can’t have a skin prick test for some reason, or results from a skin prick test aren’t clear. It can take longer to get the results of this test – sometimes days or weeks.
- Food challenges. This is when you’re given increasing amounts of certain foods to see if you have a reaction. This test is always done under supervision from a doctor or specialist nurse, and where you can be safely treated if necessary.
For some types of allergic reaction, your doctor may refer you to a dietitian to try an elimination diet. This is when you stop eating the food or foods that may be causing your allergic reaction for up to six weeks, to see whether your symptoms stop. This will only be done under the guidance of a dietitian.
Self-help for food allergies
If you’re diagnosed with a food allergy, you’ll need to avoid foods and drinks that you’re allergic to. Your doctor or dietitian will give you advice on this.
The following tips may help.
- Make sure you know exactly which foods you’re allergic to, and different terms that might be used for these on food labels.
- Check the labels on foods carefully to find out whether they contain the ingredient you’re allergic to. By law, all food companies must include a full ingredient list, clearly showing any of the 14 most common allergens on any pre-packaged foods. This also applies to foods prepared and packaged on the same premises – like a sandwich outlet or deli. Food businesses that sell ‘loose’ (unpackaged) foods must also provide information on any allergens.
- Some food products may be contaminated with tiny amounts of allergens during the production process. Many manufacturers put a warning on labels, like ‘may contain’ or ‘not suitable for’. But be aware that they have no legal requirement to include this. Products labelled as ‘free from’ a particular allergen should not contain it or have been exposed to it during manufacturing.
- Be careful not to cross-contaminate when you’re cooking or preparing foods yourself. This means keeping certain foods, knives, utensils and chopping boards separate. Always clean them straightaway.
- Take extra care when eating food that you haven’t bought or made, such as in restaurants, at school or nursery, at friends’ houses, or when travelling. Tell family and friends about your allergy and liaise with your child’s nursery or school. Check with restaurant staff how the food is prepared.
- When eating away from home, it might be helpful to wipe down surfaces before you eat, to avoid cross-contamination.
If you have a severe reaction to a food, your doctor may suggest you wear a medical emergency identification bracelet or necklace. If you have a reaction and become unwell quickly, the bracelet tells other people about your allergy, so you can get the right help quickly.
Your doctor may refer you or your child to a dietitian if you need more specialist advice on avoiding particular foods. A dietitian can also advise on reintroducing foods in children as they grow out of allergies.
Food allergy treatment
Your doctor will give you advice on how to recognise symptoms of an allergic reaction if you’re accidentally exposed to a food that affects you. They’ll also tell you how to deal with a reaction, and may suggest or prescribe some medicines you can take. These may include the following.
- Antihistamines tablets. If your allergy is mild and you only have symptoms such as itching or a rash, your doctor may suggest these. You should take them as soon as an allergic reaction starts.
- Bronchodilator inhaler. If your symptoms include wheezing or breathing problems, you might be given a medicine called an inhaler. Your doctor will tell you how much to take and when.
- Self-injectable adrenaline. If you have a severe allergic reaction to a food, your doctor may prescribe an adrenaline auto-injector (eg EpiPen or Jext). You can use this to inject yourself (or your child) in an emergency. You’ll be shown how and when to use this. Always carry it with you wherever you go.
If you have a severe reaction that affects your breathing or circulation, you should go to your nearest Accident and Emergency department. You may need hospital treatment. This may involve having adrenaline injections or an infusion in hospital.
Preventing food allergies
There has been much research into how what you eat during pregnancy and what you feed your baby may affect the risk of food allergies. The advice has changed many times during the years.
If you’re pregnant or breastfeeding, there’s no need to avoid foods that can trigger allergies. There’s no evidence that this will affect your child’s risk of developing an allergy. There’s some evidence that breastfeeding may help protect against development of allergies, but it’s not certain.
There’s no need to delay giving babies foods most likely to cause a reaction, such as eggs, cow’s milk and foods containing peanuts. This doesn’t help prevent an allergy. Newer evidence suggests giving some of these foods – including egg and peanut products – at an earlier age may be better.
UK guidance advises only giving babies solid foods, including foods like peanuts and eggs, from six months of age. Children under five shouldn’t have whole nuts, as they can cause choking. They can have finely ground nuts though, or in food as a paste (including peanut butter).
The most common food allergies include cow’s milk, eggs and peanuts. Other common food allergies include tree nuts, wheat, fish and shellfish, raw fruits and vegetables and soy. Many food allergies affecting children go away as they get older. You can read more in the common food allergies section above.
If you have a food allergy, you may get itchy, red or swollen skin around your lips, face or eyes. It can affect your breathing or give you an itchy or tingling feeling in your mouth. You might get stomach problems, like diarrhoea, sickness and vomiting too. See our food allergy symptoms section to find out more.
For allergies that have an immediate reaction, the symptoms normally go away and you’ll feel better within 12 hours. Some allergies have a delayed reaction. These come on more gradually and last for a longer time. Read more about the different types of allergy in our about food allergies section.
Current advice is to introduce solid foods to babies at around the age of six months. This includes foods that commonly cause allergy – like eggs and foods containing peanuts. There’s no reason to delay giving these foods to your baby – it doesn’t reduce the risk of developing an allergy. In fact, giving them early on may help to reduce the risk. See our preventing food allergies section for more information.
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