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What Triggers Anaphylaxis?

Last updated on 18th May 2023

Many people in the UK have allergies. In fact, the UK has some of the highest prevalence rates of allergic conditions globally, with over 20% of the population affected by one or more allergic disorder (Allergy UK). These allergies can be severe for some individuals and can sometimes result in a life-threatening allergic reaction known as anaphylaxis.

Anyone of any age can develop anaphylaxis. However, it is more common in those who suffer from allergies. According to Allergy UK, anaphylaxis-type reactions occur in approximately 1 in 1000 of the general population.

Even though anaphylaxis is relatively uncommon, the Anaphylaxis Campaign highlights that cases are on the increase.

  • The latest figures from NHS Digital reveal that hospital admissions for anaphylactic shock in adults aged 19 and over have increased 27% since last year and risen dramatically over the last seven years.
  • Hospital admissions for anaphylactic shock for adults increased from 3,751 to 4,756 from 2019 to 2020. The number of adult patients admitted to hospital because of allergies has more than doubled since 2013, reaching a record high of 27,172 in 2019/2020.

As cases of anaphylaxis are increasing, people need to be aware of the dangers and recognise the symptoms. Prompt first aid is vital in treating anaphylaxis and improving the outcome for an individual suffering from this severe allergic reaction.

There is now more awareness of anaphylaxis and the dangers. One case reported widely in the media was about Natasha Ednan-Laperouse, who died from anaphylaxis after eating a baguette containing sesame. This tragic case has led to higher protections for food allergy sufferers, which are now being written into law. This is known as ‘Natasha’s Law‘ and will come into effect later this year.

This article will cover what anaphylaxis is, the causes and the triggers. It will also look at the symptoms, treatment and prevention.

Natasha's Law Around Awareness Of Anaphylaxis And The Dangers

What is anaphylaxis, and what are the causes?

According to the NHS, anaphylaxis is a severe and potentially life-threatening reaction to a trigger such as an allergy. It develops rapidly and is a serious medical emergency that requires prompt treatment. Without medical assistance, an individual can quickly become unconscious and die. Fortunately, deaths are rare from anaphylaxis, with an estimated 20 deaths reported every year in the UK (NICE).

Anaphylaxis can be caused by many different things, which are known as triggers. If an individual comes into contact with a trigger, their immune system overreacts and sees it as harmful, even though the substance is relatively harmless. It goes into defence mode by suddenly releasing chemicals into the body, such as histamine.

These chemicals cause allergy symptoms, which are mild in most cases, e.g. someone with a runny nose and itchy eyes during hay fever season. However, for some, the release of chemicals causes anaphylaxis, which is their whole body going into overdrive in response. This overreaction of the immune system can result in life-threatening symptoms, such as breathing complications and shock.

Anaphylaxis is often referred to as anaphylactic shock. Both refer to a severe allergic reaction, but there are differences. Shock is when a person’s blood pressure drops so low that their cells and organs don’t get enough oxygen. Anaphylactic shock is a shock caused by anaphylaxis.

What increases the risk?

Some individuals will be at an increased risk of developing anaphylaxis if:

  • They are unaware of their allergies or triggers – For example, if they have never been stung by a wasp or bee before. They may also know they have allergies to particular triggers but may not be aware of others.
  • They are allergic to common triggers – It doesn’t matter if their reaction symptoms are usually mild, it can still increase the risk.
  • They have a medical history of certain types of allergies – For example, if they have asthma, allergic rhinitis or eczema. Asthma must be properly controlled to lower the risk.
  • They have had anaphylaxis before – Having anaphylaxis previously can increase the risk of future reactions. Their symptoms can worsen after every exposure.
  • They have other medical conditions – Such as heart disease and chronic lung disease.
  • They consume larger quantities of allergens – If an individual has a food allergy, the amount of food they consume (with the allergen) can influence the severity of the reaction.
  • They consume an allergen prepared in a certain way – If an individual has a food allergy, how the allergen appears in the food can influence the severity of the reaction. For example, allergens dissolved in foods can be a higher risk than those that require chewing.

In addition to the above risk factors, individuals can also be at a higher risk of developing anaphylaxis if they have been:

  • Drinking alcohol.
  • Suffering from emotional stress.
  • Ill from an infection.
  • Exercising after being in contact with a trigger.
  • Undergoing allergen immunotherapy.

What are the triggers?

Specific allergens are the most common triggers, and what triggers anaphylaxis can be different for each person. An individual does not have to be allergic to something to trigger anaphylaxis. It can occur from any foreign substance that comes into contact with the body.

Some examples of common triggers include:

  • Food, e.g. particularly those containing known food allergens, such as peanuts, tree nuts, shellfish and sesame.
  • Medications, e.g. antibiotics, such as penicillin, and non-steroidal anti-inflammatory pain medicines (NSAIDs), such as ibuprofen.
  • General anaesthetic.
  • Contrast agents, e.g. dyes used in scans and X-rays.
  • Latex, e.g. in rubber gloves.
  • Insect stings and bites, e.g. venom in wasp and bee stings.

According to NICE, food is a common trigger in children, while medicinal products are much more common triggers in older people. In the UK, it is estimated that 500,000 people have had a venom-induced anaphylactic reaction and 220,000 people up to the age of 44 have had a nut-induced anaphylactic reaction.

Anaphylaxis can also be caused by less common triggers. For example, it can occur during or after physical activity, which is known as exercise-induced anaphylaxis. It can also happen as a result of hormonal changes.

Sometimes, there is not always an obvious trigger for the reaction. In these cases, it is known as idiopathic anaphylaxis.

Common Trigger Of Anaphylaxis

What are the symptoms of anaphylaxis?

When someone with an allergy comes into contact with an allergen, it produces an abnormal immune response in the body.

The flood of chemicals from the immune system’s response can result in mildly irritating symptoms for some people, for example:

  • Tingling or itching of the lips and inside the mouth.
  • Hives (rash), warmth, paleness, flushing and itchiness of the skin.
  • Swelling of the face, eyes, lips or other body parts.

In others, they may experience an anaphylactic reaction. Symptoms of anaphylaxis usually develop rapidly, i.e. within a few minutes. However, in some cases, they can take a few hours and can even re-develop in some people.

The symptoms of anaphylaxis include:

  • Other allergy symptoms as above, but more severe. These tend to develop first.
  • Swollen tongue and throat.
  • Breathing difficulties, wheezing and coughing.
  • Nausea, vomiting, diarrhoea and stomach cramps.
  • Difficulty swallowing or speaking.
  • Bluish tinge to the lips and tongue.
  • Increased heart rate and palpitations.
  • Clammy skin.
  • Dizziness or lightheadedness due to a sudden drop in blood pressure.
  • Confusion, irritability and anxiety.
  • A sense of impending doom.
  • Collapsing and unconsciousness.

Some of the above symptoms occur when anaphylaxis progresses to anaphylactic shock. The individual can become unresponsive and may even go into cardiac arrest if left untreated.

Symptoms of an allergic reaction can be milder in some people and may subside on their own. However, anaphylaxis is life-threatening, and the symptoms are likely to be severe, as the whole body is affected. If an individual does not receive medical attention promptly, it can cause complications and can be fatal. Knowing the symptoms of anaphylaxis can save lives.

What to do if an individual is showing signs of anaphylaxis symptoms?

If an individual is showing signs of anaphylaxis symptoms, it is vital to act immediately to give them the best chances of survival.

Prompt first aid is essential and should include the following steps:

  • Use an adrenaline (epinephrine) auto-injector – If an individual has an adrenaline auto-injector, help them administer it or use it for them if they cannot do so themselves. The injection is given into the upper outer muscle of the thigh. Allergy UK recommends not hesitating to use it if required, as adrenaline given in this way is a safe treatment and can save lives.
  • Call for an ambulance – Even if the individual starts to feel better and their symptoms start to clear, immediately call 999 and ask for an ambulance. Inform the operator that you suspect it is anaphylaxis and follow any instructions given.
  • Remove the trigger – If possible, remove the cause of the reaction. For example, if a person has been stung by a wasp and the stinger remains, try and remove it carefully.
  • Lie them down flat – This helps the individual maintain their blood pressure and avoids injury if they collapse. Other positions may be necessary for certain people, for example:
    – If they are unconscious – recovery position.
    – If they are pregnant – lie on their left side.
    – If they are struggling with their breathing – sit up.
  • Use another adrenaline auto-injector – If the individual has a second injector available and their symptoms have not improved after the first injection, administer another dose after 5 minutes.

If the individual having anaphylaxis is able, they can follow the above steps themselves. If they are unresponsive and not breathing, CPR should commence immediately.

There are first aid courses available that specifically cover the actions to take if an individual develops anaphylaxis. Further information is also available on the Allergy UK website.

What are the treatments?

The main treatment for anaphylaxis is adrenaline. If an injector is available during first aid, this will improve the prognosis for the individual. Those who are known to be at an ongoing risk should have at least two immediately available injectors.

All individuals with anaphylaxis should be taken to the hospital. Once there, they may have blood tests to confirm that it is anaphylaxis.

They may also be given other medication, as well as adrenaline, to help improve their symptoms, such as:

  • Antihistamines, which block the action of histamine and relieve allergy symptoms.
  • Steroids to prevent the development of delayed anaphylaxis.
  • Intravenous fluids to help increase blood pressure.
  • Oxygen to help with breathing.

They will also have to be observed for up to 24 hours, as symptoms can sometimes return. Only when the individual’s symptoms are under control, and it is unlikely they will return, will they be allowed to go home.

An individual hospitalised with anaphylaxis will likely be referred to an allergy specialist who may carry out allergy tests and advise on preventing it from recurring.

On discharge from the hospital, the individual may also be prescribed antihistamines and corticosteroids to prevent symptoms from returning and adrenaline auto-injectors for use in an emergency.

An Injector of Adrenaline To Improve The Prognosis With Anaphylaxis

Preventing anaphylaxis

It is always better to prevent anaphylaxis rather than treating it. Even though the number of fatalities is small, a severe allergic reaction is still a frightening experience for an individual, and the symptoms are highly unpleasant. There is also a risk of complications with anaphylaxis, so it is always best to avoid this life-threatening allergic reaction wherever possible.

There are many things people can do to prevent anaphylaxis. They can:

Identify the triggers

Different tests can identify whether an individual has any allergies. Doctors will usually refer them to a specialist allergy clinic if they have had anaphylaxis but the trigger is unknown.

There are two main types of test to identify triggers, which are:

  • Skin allergy test – Involves lightly pricking the skin with a tiny amount of an allergen to observe whether there is a reaction.
  • Blood test – Involves testing an individual’s blood in a laboratory for the amount of IgE (allergy) antibodies in response to an allergen.

If an individual’s triggers are identified, and an allergy is diagnosed, it can help them avoid future anaphylactic reactions.

Avoid the triggers

If an individual is aware of what their triggers are, they must take steps to avoid them.

For example:

  • If an individual has a food allergy, they should:
    – Carefully read food and drink labels to ensure they do not contain allergenic ingredients that can trigger symptoms.
    – Be vigilant when eating out by informing staff they have an allergy and ask about the ingredients before ordering. Even trace amounts of an allergen can result in a reaction, so it is crucial to consider cross-contamination when eating out.
  • If an individual has an allergy to certain medicines, they should:
    – Inform all healthcare professionals of any allergies to medicines, as they may not know.
    – Be prescribed alternative medicines, e.g. a doctor may prescribe different antibiotics as an alternative to penicillin.
  • If an individual is allergic to insect stings, they should:
    – Remain calm around stinging insects and don’t anger them by trying to swat them away.
    – Avoid strong-scented perfumes, aftershaves, sprays and creams.
    – Wear long-sleeved tops and trousers, which are not brightly coloured.
    – Not walk around outside with bare feet.
    – Not drink sugary drinks from open cans outside, as wasps can fly in without them noticing.

Avoiding triggers is an important part of allergy management.

Manage underlying medical conditions

If an individual has a heart condition or asthma, these must be managed and controlled, as there is an increased risk of complications and death in the event of anaphylaxis.

If they are on any medication for an underlying medical condition and have allergies, it mustn’t interfere with adrenaline and make it less effective. Individuals should discuss this with their GP.

Allergen immunotherapy

Individuals can attend specialist clinics, which provide immunotherapy for desensitisation. This involves exposing them to the smallest amounts of the allergen and increasing the doses over time under controlled conditions. The aim is to make their immune system less sensitive to the allergen.

Immunotherapy is not necessarily a cure, but it can reduce the severity of allergy symptoms. However, there is a risk of anaphylaxis during treatment, especially if the doses given are too high.

Carry adrenaline auto-injectors

Individuals at high risk of developing anaphylaxis will be prescribed adrenaline auto-injectors. If this is the case, the individual should ensure that two injectors are close by at all times.

They should avoid storing them in a place where it is too hot or too cold and must regularly check the expiration dates. If any have expired, it is vital to get replacements quickly.

Tell people around them

Family and friends should already be aware of an individual’s allergies. However, it is also vital to inform employers, as they have a legal duty to provide first aid to employees. First-aiders should know where the individual’s adrenaline auto-injectors are.

If people are informed about a person’s allergies, they can help them to avoid triggers.

Wear a medical alert bracelet or necklace

If an individual is at risk, they can wear a medical bracelet or necklace to alert others in the event of anaphylaxis. It can also help prevent a severe reaction if the individual is taken ill and cannot inform paramedics and hospital staff of their allergies. If healthcare professionals are unaware of their allergies in an emergency, they could provide treatments that could cause anaphylaxis.

As an alternative to bracelets and necklaces, individuals can also carry emergency medical cards.

It is not always possible to prevent anaphylaxis, but if an individual identifies and manages their allergies properly, it can significantly reduce the risk.


Allergies are on the rise in the UK, and so is anaphylaxis. Administering prompt first aid to an individual with anaphylaxis can save their life. Therefore, it is crucial to be aware of the symptoms and act quickly. The actions a person takes are critical in reducing the risk of anaphylactic shock and death.

With anaphylaxis, prevention is better than the cure, as symptoms can be very unpleasant and may quickly become life-threatening without prompt treatment. In most cases, anaphylaxis can be prevented by identifying and avoiding triggers and having vital adrenaline auto-injectors close by in the event of a severe reaction.

Why not take our Institute of Hospitality approved Anaphylaxis Awareness Course to learn more about allergies and anaphylaxis.

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About the author

Michelle Putter

Michelle Putter

Michelle graduated with an MSc in wildlife biology and conservation in 2012, but her career has taken quite a different turn to the one expected. She started in health and safety in 2009 and has worked in several industries such as electrical engineering, aviation and manufacturing. She has been working with CPD Online College since 2018 and became NEBOSH Diploma qualified in 2020. In her spare time, Michelle's passions are wildlife and her garden. She has volunteered for many conservation organisations and particularly enjoys biological recording. Michelle also likes hiking, jogging and cycling.

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