What is anaphylaxis?

Anaphylaxis is the name given to an extreme form of allergic reaction. Typically, it occurs very suddenly and without warning. The symptoms get rapidly worse and, without treatment, can cause death. The symptoms affect many parts of of the body’s.

What happens in an anaphylactic reaction?

An allergy is a response by the body’s immune system to something (called an allergen) that is not necessarily harmful in itself. Certain people are sensitive to this allergen and have a reaction when exposed to it.

During an allergic reaction, a complex series of events occurs within the body. These events are co-ordinated by the immune system. Sometimes the immune system ‘goes into overdrive’. If this happens, the body can lose control of its vital functions, with catastrophic results. Such a severe reaction can cause death. This is anaphylaxis.

On a more detailed level, changes happen within the walls of capillaries, the smallest blood vessels in the body. The capillaries become leaky, and fluid leaks from the blood into the tissues (blood is comprised of blood cells as well as fluid called serum). So much fluid is lost from the vascular (blood) system, that blood pressure falls. As the blood pressure drops, there is a lack of blood to the major organs. This is known as shock – and in this case is anaphylactic shock.

(See separate leaflet called ‘Allergy – General Overview’ for more information on allergic reactions, including details of allergens and the immune system response.)

What causes anaphylaxis?

Anaphylaxis can potentially be caused by any allergen. Most allergens are proteins, but some (such as medications) are not. Many cases of anaphylaxis have no known cause. This is referred to as idiopathic anaphylaxis.

Causes of anaphylaxis:

  • Idiopathic (unknown).
  • Food – common examples include nuts (for example, peanut, brazil), shellfish and eggs.
  • Venom, for example, bee or wasp stings.
  • Medicines – common examples include:
    • Antibiotics, for example, penicillin.
    • Painkillers, for example, opioids such as morphine or codeine, or non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin.

How common is anaphylaxis?

We do not know exactly how common anaphylaxis is. This is because some people having an anaphylactic reaction are not correctly diagnosed. This is because some of the symptoms of anaphylaxis can be similar to other medical problems – for example, a severe asthma attack. Sometimes people are recognised as having a significant allergic reaction and are treated in hospital, but the event is never properly identified or recorded as anaphylaxis.

It is estimated that there are between 1 and 3 cases of anaphylaxis in every 10 000 people, every year in the UK. It is estimated that about half a million people in the UK have had an anaphylactic reaction to venom (bee or wasp stings), whilst almost a quarter of a million people under 44 years of age have had anaphylaxis due to nuts.

About 20 people a year die in the UK due to anaphylactic reactions. In about half of these cases, there is no known cause (idiopathic anaphylaxis).

Who gets anaphylaxis?

It is mainly children and young adults who are affected by anaphylaxis. Food is a common cause in children, but medicines seem to be more common triggers in adults. Anaphylactic reactions appear to be more common in females.

What are the symptoms of anaphylaxis?

Classic early symptoms of anaphylaxis include:

  • Wheezing and hoarseness. This happens as the airways narrow.
  • Swelling of the lips, tongue and throat. It is known as angio-oedema. The swelling involves the deeper layers of the skin. Whilst it can occur around the eyes, and in the hands and feet, it is more significant when it affects the lips, tongue and throat. Swelling here can completely block your airway, meaning air (and therefore oxygen) cannot be breathed into the lungs. Without emergency treatment, this results in asphyxiation (suffocation).
  • An itchy rash, like nettle rash – commonly called hives. Urticaria is the medical term. The rash is raised and generally pale pink in colour. The raised areas are called wheals. Not everyone having an anaphylactic reaction gets this rash.

Other symptoms include:

  • Feeling faint – due to dropping of your blood pressure.
  • A sense of impending doom.
  • A fast heart rate (tachycardia) or palpitations as your heart tries to pump faster to maintain your blood pressure.
  • Symptoms involving the gastrointestinal tract (the gut). These include nausea, vomiting and abdominal pain.

Classic advancing symptoms of anaphylaxis include:

  • Stridor. This is a noise created by trying to breathe in when the upper airways (namely the mouth, throat and upper windpipe (trachea)) are obstructed. This is due to swelling in these tissues.
  • Respiratory collapse. This means that the respiratory (breathing) system of the body is failing. There might be fast, shallow breathing and the skin of the lips and tongue may become bluish (called cyanosis). If you cannot breathe air into the lungs, the blood cannot be oxygenated. Oxygenated blood is needed so that the cells in our body, and therefore the organs in our body, can work. It is vitally important that the brain should not be starved of oxygen. The heart muscle needs oxygen so it can pump the blood round the body. Once one major organ system of the body starts to falter, in turn the others become strained until they are unable to function too. Death is the result of such a catastrophic ‘systems failure’.
  • Confusion, agitation, anxiety and loss of consciousness. These symptoms soon follow. Low oxygen levels (hypoxia) can make you confused. If you are unable to breathe properly due to angio-oedema, you will feel restless and anxious – you are effectively suffocating. Eventually, loss of consciousness occurs.
  • Low blood pressure (hypotension) and eventual circulatory collapse are the end events.

Do I need any tests for anaphylaxis?

Anaphylaxis is primarily a clinical diagnosis. This means that it is diagnosed based on the recognition of symptoms and the manner in which they occur – that is, quickly and rapidly worsening.

Anaphylaxis does need to be distinguished from other medical conditions that may have some similar symptoms. These include a life-threatening asthma attack, or a severe blood infection (septic shock). There are also other conditions that are not life-threatening but that can initially seem similar to anaphylaxis. Examples include panic attacks, fainting (vasovagal episode) or idiopathic (non-allergic urticaria) or angio-oedema. (see separate leaflets called ‘Acute Urticaria’ and ‘Angio-oedema’ for more information.

A blood test can be done to identify anaphylaxis and rule out other causes for the symptoms. The blood test measures mast-cell tryptase. This is a chemical released by mast cells (a type of cell in the immune system) during a severe allergic reaction. Levels rise to a maximum within an hour of an anaphylactic reaction. Levels remain elevated for six hours.

It is important to realise that the treatment for anaphylaxis is an emergency, so anyone with presumed anaphylaxis is treated as such. The blood test has no role in the immediate management of someone with a severe allergic reaction. After life-saving emergency treatment has been started and the situation is stable, this blood test can be taken. It is suggested to take one sample as soon as possible and another 1-2 hours after the anaphylactic reaction. A further sample can be taken once recovery is complete, or even at a follow-up appointment in an allergy clinic.

What is the treatment for anaphylaxis?

Anaphylaxis is a life-threatening emergency and needs to be treated in a hospital.

First aid measures for anaphylaxis (out of hospital) include:

  • Administration of an adrenaline auto-injector (if there is one). This is a pre-filled syringe with a needle – sometimes referred to as an adrenaline pen. The idea is that it can be injected by the person having the anaphylactic reaction (if there is time), or by a bystander who knows how to use it.
  • Cardiopulmonary resuscitation (CPR) if the person is unresponsive and not breathing. If you are not medically trained or have not been taught how to to perform CPR with rescue breaths, the new advice is to give Hands-only CPR. This means you do not have to give mouth to mouth resuscitation (also called the kiss of life). If a person is found collapsed and is not breathing, after calling the emergency services, all you have to do is chest compressions. The idea behind this is simple – chest compressions are better than nothing, and many people are put off by the idea of mouth to mouth. Hands-only CPR is unlikely to bring someone out of cardiac arrest (the heart has stopped). However, it will pump some blood round the body, importantly the brain will get some oxygen from the blood it receives. (See below under ‘Further help and advice’ for details of hands-only CPR.)

Hospital treatment:

  • People with presumed anaphylaxis are treated in the resuscitation room of an emergency department (ED).
  • The main treatment is still adrenaline, usually given by injection into the muscle of the thigh (called an intramuscular (IM) injection).
  • Resuscitation of someone having an anaphylactic reaction follows an ordered sequence – ABC:
    • A stands for Airway. An airway is essential to life – so that we can breathe. A swollen tongue from angio-oedema can block the airway. People with anaphylaxis are nursed lying flat. Sometimes a tube is needed to help keep the airway open.
    • B stands for Breathing. Oxygen is given with a face mask, or, if the patient has a tube for breathing, down that.
    • C stands for Circulation. Intravenous access – a ‘drip’ is needed for fluids and other medicines. Fluids may help to keep up the blood pressure and maintain blood circulation around the body.
  • The specifics of treatment do depend on how well or unwell the person with anaphylaxis is. There is a great deal of difference between treating someone who is unconscious and in cardiac arrest (so needs resuscitation) and someone who is in the early stages of anaphylaxis. However, the point is that anaphylaxis progresses rapidly. ABC still needs to be considered before deterioration occurs.
  • Other medicines used to treat anaphylaxis include antihistamines and hydrocortisone (a type of steroid). Sometimes a nebuliser is used. This is often a type of treatment given to people having an asthma attack. A medicine called salbutamol is inhaled like a fine mist, through a mask. It helps to open up (bronchodilate) tight airways in the lungs.
  • Whilst treatment is ongoing, a person with anaphylaxis will be closely monitored. This involves (amongst other things) blood pressure monitoring, heart monitoring and an electrocardiogram (ECG or heart trace) and measurement of the oxygen levels in the blood (using a pulse oximeter to measure oxygen saturation – sats).
  • If you have had an anaphylactic reaction, you will be kept in hospital for a minimum of 6-8 hours, to monitor your condition. Such a short admission is only appropriate if you recovered quickly and without complication. In other cases, admission and monitoring will continue longer. Children with anaphylaxis would normally be admitted to a paediatric (children’s) ward and kept in hospital for a bit longer. There is a small risk of a problem called a biphasic reaction. This is where there is a delayed anaphylactic reaction, some 4-10 hours later.

What is the outlook for anaphylaxis?

If you have had a confirmed anaphylactic reaction, you should be referred to an allergy specialist. Generally you would be seen in a hospital outpatient clinic by a consultant immunologist.

As an outpatient, further blood tests and other tests for allergies may be done. An example would be skin prick testing. (See separate leaflet called ‘Skin Prick Allergy Test’ for more information.) It is also very likely that you would be prescribed an adrenaline auto-injector device, such as those described below. You would be taught how to use one and be provided with written information on what to do in the event of a further anaphylactic reaction.

If you have a history of anaphylaxis, it might be a good idea to purchase a Medic-Alert® bracelet or necklace (or similar). Any medically trained person, including paramedics, checks to see if a collapsed patient is wearing such an item. (See below under ‘Further help and advice’ for details of MedicAlert®.)

What should I do if I think someone is having an anaphylactic reaction?

Anaphylaxis is likely when:

  1. There is a sudden onset of symptoms.
  2. Symptoms get rapidly much worse.
  3. There are life-threatening airway and/or breathing problems and/or circulation problems.
  4. There are skin changes such as swelling of the lips and tongue (angio-oedema), hives (urticaria) and flushing.

The person may have had a severe allergic reaction or anaphylaxis in the past. However, this may be the first time.

A person having difficulty breathing may prefer to sit up in a chair. It is best, for a person feeling faint, to lie down.

  1. Look to see if the person is wearing a MedicAlert® bracelet or necklace (or similar). Are they carrying an adrenaline pen? These are also called adrenaline auto-injectors. Brands include: EpiPen®, Anapen® and Juxta®. If they are, you could save their life by administering it. Techniques for injection vary slightly, according to the device prescribed (see below). Each device is designed to be used only once – you cannot repeat the procedure with a used auto-injector.
  2. Call 999 for an ambulance – act quickly as anaphylaxis is a medical emergency.

Should I carry an adrenaline pen just in case?

If you have had an anaphylactic reaction, you should be prescribed an adrenaline auto-injector and taught how to use it. If for any reason you would be unable to use such a device (for example, children, those with some physical disabilities or learning difficulty), parents or carers should be instructed.

One of the most important things is that you carry the auto-injector with you at all times – in your bag or about your person.

If your child has anaphylaxis, schools may wish to keep an adrenaline auto-injector there. However, it is still vitally important your child should personally carry a device – there’s no point in it being locked in a medicine box and being in the medical bay and inaccessible if anaphylaxis happens in the classroom. Sensible measures should be taken – for very young children, it may be appropriate for the teacher to have the auto-injector. Teachers of children with a history of anaphylaxis should also be trained in how to administer adrenaline auto-injectors.

Wouldn’t it be safer to have several adrenaline pens on prescription from my GP?

If you have had an anaphylactic reaction in the past you should ensure you do not become complacent about it. If you are prescribed an adrenaline auto-injector, you should carry it with you at all times.

This is one reason why some doctors may refuse to prescribe multiple auto-injector devices. Many people think that having one in multiple places is safer, but actually the reverse is true. It is better to have one (or maybe two) and look after them carefully. You don’t want to be in the one place you haven’t kept a device when you have an anaphylactic reaction.

Device failure is exceedingly uncommon, so a back-up adrenaline auto injector is not really needed.

Multiple devices also mean it is harder to keep track of the expiry dates on the adrenaline, and can lead to a lot of waste when they need to be replaced. Most auto-injectors are (thankfully) disposed of, unused.

Adrenaline auto-injector use

Note: the following is a guide. It is not intended as a substitution for proper training and instruction. Dummy devices exist that can be practised with (they do not contain any adrenaline or have a needle).

To use Anapen®

  • Remove the black needle cap.
  • Remove the black safety cap from the firing button.
  • Hold Anapen® against the outer thigh and press the red firing button. Note the injection can be given through clothing if necessary.
  • Hold Anapen® in position for 10 seconds. This allows the full dose of adrenaline to be injected.
  • Make sure you tell the paramedics that an adrenaline pen has been given.

For more information on how to give Anapen®, see:
Web: www.anapen.com

To use EpiPen®

  • Pull off the blue safety release cap at the end.
  • Hold the pen firmly and swing your arm to push the orange tip against the outer thigh. Note the injection can be given through thin clothing such as trousers, skirts or tights.
  • The ‘injection’ will be fired automatically into the thigh muscle.
  • Hold the orange tip against the thigh for 10 seconds.
  • As soon as you release pressure, a protective cover will extend over the needle tip.
  • Make sure you tell the paramedics that an adrenaline pen has been given.

For more information on how to give EpiPen®, see:
Web: www.epipen.com/how-to-use-epipen.

To use Jext®

  • Remove the Juxta® from its flip-top case.
  • Grasp the pen in your dominant hand with your thumb closest to the yellow cap.
  • Pull off the yellow cap with your other hand.
  • Push black tip firmly into your outer thigh until you hear a click, confirming the injection has started, and keep it pushed in.
  • Hold the injector in place against the thigh for 10 seconds, then remove.
  • The needle shield will automatically cover the needle when the Juxta® is removed from the thigh.
  • Massage the area for 10 seconds.
  • Make sure you tell the paramedics that an adrenaline pen has been given.

For more information on how to give Juxta®, see:
Web: www.jext.co.uk/jext-video-demonstrations.aspx

Further help and advice

The Anaphylaxis Campaign

A UK charity providing information and support to people at risk from severe allergic reactions.
PO Box 275, Farnborough, GU14 6SAX
Helpline: 01252 542029
Web: www.anaphylaxis.org.uk

Allergy UK

The UK’s leading medical charity dealing with allergy.
No 3 White Oak Square, London Road, Swanley, Kent, BR8 7AG
Tel: 01322 619898 Allergy Help Line: 01322 619864
Web: www.allergyuk.org

Resuscitation Council (UK)

The professional group providing education and reference materials to healthcare professionals and the general public in the most effective methods of resuscitation.
5th Floor, Tavistock House North, Tavistock Square, London WC1H 9HR
Web: www.resus.org.uk


A non-profit-making, registered charity providing a life-saving identification system for individuals with hidden medical conditions and allergies.
The MedicAlert Foundation,1 Bridge Wharf,156 Caledonian Road, London N1 9UU
Freephone tel: 0800 581420
Emergency telephone (not for general queries or administration): 0207 407 2818
Web: www.medicalert.org.uk

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