Food allergy and anaphylaxis
Also known as: food allergies, nut allergy, peanut allergy, milk allergy, egg allergy
A food allergy is when the immune system overreacts to certain foods, with reactions that range from mild to life-threatening anaphylaxis.
When to seek care
Call 999 for suspected anaphylaxis, such as swelling of the throat or tongue, difficulty breathing, or feeling faint or confused, and say it is anaphylaxis. The NHS says to use an adrenaline auto-injector if one is available. For symptoms that keep coming back after eating a food, the NHS advises seeing a GP.
Overview
A food allergy happens when the immune system overreacts to certain foods. The NHS lists itchy skin or hives, swelling of the lips, face and eyes, breathing difficulties, feeling sick and tummy pain among the symptoms. A food allergy is different from a food intolerance, which does not involve the immune system. Children are most often allergic to milk, eggs, peanuts and tree nuts. Anaphylaxis is a life-threatening allergic reaction that happens very quickly and needs emergency treatment.
Causes
- The immune system overreacts to certain foods.
- Why the immune system reacts to a food is not fully understood.
- The NHS lists nuts, milk, eggs, shellfish, fish, sesame seeds and kiwi fruit among common food triggers of anaphylaxis.
Risk factors
- A family history of allergies, asthma or eczema raises the risk slightly.
- Allergy UK says the risk can be higher when another allergic condition, such as eczema, is present.
Symptoms
What a clinician may find
- Itchy skin or hives, and swelling of the lips, face and eyes.
- Feeling sick, tummy pain and diarrhoea.
- Breathing difficulties, and in a severe reaction wheezing and swelling of the throat and tongue.
Complications
- Anaphylaxis, a life-threatening allergic reaction.
- Symptoms of anaphylaxis can return hours after the first reaction, known as a biphasic reaction.
Diagnosis
The NHS lists skin-prick tests, blood tests and sometimes an elimination diet. NICE guidance for under 19s says to offer a skin prick test or blood tests for specific IgE antibodies when IgE-mediated allergy is suspected. For suspected non-IgE-mediated allergy it recommends a trial elimination of the suspected food. A GP may refer to a specialist.
Treatment
The NHS says the main approach is avoiding the food. Antihistamines are used for mild reactions, while adrenaline auto-injectors are for severe ones, and antihistamines do not replace adrenaline in anaphylaxis. A specialist gives an allergy action plan, a written set of instructions for managing a reaction. Anaphylaxis is treated in hospital straight away, with adrenaline, oxygen and fluids given into a vein.
Prevention
The NHS advises checking food labels carefully and telling staff at restaurants and cafes about the allergy. NHS guidance for babies says waiting beyond 6 to 12 months to introduce peanut and egg may raise the risk of allergy.
Key facts
| Fact | Detail |
|---|---|
| Also called | Nut allergy, peanut allergy, milk allergy and egg allergy are common types |
| Usually diagnosed by | Skin prick or blood tests, sometimes an elimination diet |
| Most common in children | Milk, eggs, peanuts and tree nuts |
| Often outgrown | Milk, egg, soy and wheat allergies that start early in life |
| Emergency route | Call 999 for suspected anaphylaxis |
| Reaction timing | Immediate reactions occur seconds or minutes after eating; others can be delayed by days |
What is a food allergy?
A food allergy happens when the immune system overreacts to certain foods. Reactions range from mild to life-threatening anaphylaxis. Why the immune system reacts to a food is not fully understood. A food allergy is different from a food intolerance. The NHS says a food intolerance does not involve the immune system, so it cannot cause a serious allergic reaction. Intolerance symptoms, such as bloating, wind, diarrhoea and tummy pain, usually appear a few hours after eating the food.
A family history of allergies, asthma or eczema raises the risk slightly. Allergy UK says the risk can be higher when another allergic condition, such as eczema, is present.
Some people have a mix of immediate and delayed reactions to the same food. Immediate reactions are called IgE-mediated, and delayed ones are called non-IgE-mediated. Allergy UK says non-IgE-mediated reactions do not involve IgE antibodies and have a delayed onset.
What are the symptoms of a food allergy?
The NHS lists itchy skin or hives, swelling of the lips, face and eyes, breathing difficulties, feeling sick, tummy pain and diarrhoea. Symptoms may start straight after eating the food, or days later.
Allergy UK says symptoms of an immediate, IgE-mediated food allergy occur a few seconds or minutes after eating. Allergy UK also describes a type with both immediate symptoms, such as hives or swelling, and delayed symptoms, such as gut or skin problems. Immediate IgE-mediated reactions carry the risk of anaphylaxis.
A severe reaction is called anaphylaxis, which starts quickly and can cause breathing problems. NHS Scotland says a reaction may start mild and progress rapidly to severe. The NHS says to call 999 for signs such as sudden confusion or drowsiness, fainting, or a child who goes limp and floppy.
Which foods most often cause allergic reactions?
In children, the most common food allergies are to milk, eggs, peanuts and tree nuts. Allergy UK says food allergy in UK adults more commonly involves peanuts, tree nuts, crustaceans and plant foods. The NHS lists nuts, milk, eggs, shellfish, fish, sesame seeds and kiwi fruit among common food triggers of anaphylaxis. Anaphylaxis UK says milk, egg, soy and wheat allergies that start early in life are often outgrown. Peanut and tree nut allergies are much less likely to be outgrown, and fish and shellfish allergies also tend to last.
A Food Standards Agency study, reported by Anaphylaxis UK, estimated that around 6% of UK adults, about 2.4 million people, have a clinically confirmed food allergy. In the first stage of that study, over 30% of adults reported some type of adverse reaction when eating food, but the clinical follow-up narrowed this to about 6%.
How is a food allergy diagnosed?
The NHS lists skin-prick tests, blood tests and sometimes an elimination diet among the ways a food allergy is investigated. A GP may refer to a specialist.
The NICE guideline on food allergy in under 19s says that when IgE-mediated allergy is suspected, a skin prick test or blood tests for specific IgE antibodies should be offered. Skin prick tests should only be done where there are facilities to manage an anaphylactic reaction. For suspected non-IgE-mediated allergy, the guideline recommends a trial elimination of the suspected food, followed by reintroduction. The NICE guideline says that serum-specific IgG testing, the vega test, applied kinesiology and hair analysis should not be used to diagnose food allergy.
NICE advises considering referral to specialist care for children who have had an acute systemic reaction or a severe delayed reaction, or who may have multiple food allergies.
How is a food allergy treated and managed?
The NHS says the main approach to food allergy is avoiding the food that causes it. Antihistamines are used for mild reactions, while adrenaline auto-injectors are for severe ones. Antihistamines do not replace adrenaline in a severe reaction. A specialist gives an allergy action plan, a written set of instructions for managing a reaction.
Day-to-day management involves checking food labels carefully and telling staff at restaurants and cafes about the allergy, according to the NHS.
For babies, NHS guidance says common allergenic foods can be introduced from about 6 months, one at a time and in very small amounts so that any reaction can be spotted. The NHS says waiting beyond 6 to 12 months may raise the risk of peanut and egg allergy. For babies with eczema or an existing food allergy, or with a family history of allergy, the NHS advises talking to a GP or health visitor first.
What is anaphylaxis and what happens in an emergency?
Anaphylaxis is a life-threatening allergic reaction that happens very quickly. Signs can appear within minutes of contact with the trigger. They include swelling of the throat and tongue, difficulty breathing, wheezing, feeling faint or confused, and blue, grey or pale skin.
The NHS says to call 999 and say it is anaphylaxis. It also says to use an adrenaline auto-injector if one is available. The NHS describes lying down with the legs raised if feeling faint, or sitting up if breathing is difficult.
Anaphylaxis is treated in hospital straight away, with adrenaline, oxygen and fluids given into a vein. The NHS says people usually stay in hospital for around 2 to 12 hours. Before leaving hospital, people should be given 2 adrenaline auto-injectors or a prescription for them.
Symptoms of anaphylaxis can return hours after the first reaction. NHS Scotland calls this a biphasic reaction.
Frequently asked questions
What is the difference between a food allergy and a food intolerance?
A food allergy involves the immune system and can cause itchy skin or hives, swelling, breathing difficulties and tummy problems. A food intolerance does not involve the immune system, so it cannot cause a serious allergic reaction. The NHS says intolerance symptoms usually appear a few hours after eating and often include bloating, wind, diarrhoea and tummy pain.
Can children grow out of a food allergy?
Anaphylaxis UK says milk, egg, soy and wheat allergies that start early in life are often outgrown. Peanut and tree nut allergies are much less likely to be outgrown, and fish and shellfish allergies also tend to last. Anaphylaxis UK publishes a factsheet called Outgrowing childhood food allergy.
Can a food allergy cause anaphylaxis?
Yes, the NHS says anaphylaxis can be caused by food, medicines or insect stings. It is life-threatening and happens very quickly. The NHS says to call 999 and to use an adrenaline auto-injector if one is available. Hospital treatment can include adrenaline, oxygen and fluids given into a vein.
How common is food allergy in the UK?
A Food Standards Agency study reported by Anaphylaxis UK estimated that around 6% of UK adults, about 2.4 million people, have a clinically confirmed food allergy. In the first stage of the study, over 30% of adults reported some type of adverse reaction when eating food, so more adults report reactions than have a confirmed allergy.
How is an elimination diet used to diagnose a food allergy?
For suspected non-IgE-mediated allergy, the NICE guideline recommends a trial elimination of the suspected food, followed by reintroduction. The NHS lists an elimination diet among the ways a food allergy may be investigated, alongside skin-prick tests and blood tests. A GP may refer to a specialist. NICE says serum-specific IgG testing should not be used to diagnose food allergy.
Connected pages in detail
What each linked page on Anatomy Nexus covers, in a line, for Food allergy and anaphylaxis.
Conditions
- Asthma A chronic inflammatory disease of the airways causing reversible narrowing, with episodes of wheeze, breathlessness, chest tightness and cough.
Symptoms
- Rash Any change in the colour or texture of the skin.
- Swelling (oedema) Excess fluid in the tissues.
- Shortness of breath The sensation of not getting enough air.
- Nausea The unpleasant sensation of being about to vomit.
- Abdominal pain Pain between the ribs and the pelvis.
Guides and news
- Anaphylaxis and adrenaline auto-injectors Anaphylaxis is a severe allergic reaction; the NHS describes adrenaline, calling 999 and hospital care.
- MHRA consults on school adrenaline sprays The MHRA has opened a UK-wide consultation on letting schools buy and keep spare adrenaline nasal sprays for emergencies, alongside auto-injectors.