• Tim


Updated: Sep 23, 2021

Anaphylaxis is a type of potentially life-threatening allergic reaction. Every year in the UK, there are somewhere in the region of 5,000 emergency anaphylactic reactions that lead to hospitalisation.

Fortunately, there are only around 20 deaths, with approximately half of these caused by medical treatments. When anaphylaxis is fatal, death usually occurs very soon after contact with the trigger, usually within the first hour, peaking at about 30 minutes.

It is thought that approximately 80% of anaphylactic reactions would not be life-threatening, even with no treatment.

The number of anaphylactic reactions have rapidly increased in recent decades. Over the period 1992-2012, there was a 7-fold increase in the number of reactions. We don't yet know why this is.

This blog explores the first aid treatment for anaphylaxis and what separates it from a less severe allergic reaction.

What is Anaphylaxis?

Anaphylaxis is a severe, systemic, hypersensitivity reaction. It has common features, which may include rapidly developing airway, breathing and circulation problems, as well as skin changes and digestive system problems.

Some people are at higher risk of having an anaphylactic reaction. Including if they have:

  • Had a mild or moderate allergic reaction previously

  • A related condition, such as asthma, eczema or hayfever

  • Repeated exposure to an allergen

Anaphylaxis can be caused by an inappropriate immune system reaction, or through other mechanisms. Food, insect venom, some drugs and latex can cause a reaction through the immune system, but most drug-induced reactions are through non-immune system mechanisms.

There are a significant proportion of anaphylactic reactions where there is no identifiable cause, known as idiopathic anaphylaxis.

What Triggers an Anaphylactic Reaction?

The triggers for anaphylaxis vary considerably with age. For example, food is a particularly common trigger in young people, while pharmaceutical drugs tend to be a more common trigger in older people.

The specific triggers for anaphylaxis are many and varied, and include:

  • Food (including nuts and some fruits such as strawberries and kiwi)

  • Insect stings (particularly wasps and bees)

  • Medication (including some antibiotics, NSAIDs, aspirin and general anaesthetic)

  • Latex

When is an Allergic Reaction deemed to be Anaphylaxis?

Defining the signs and symptoms of an anaphylactic reaction is notoriously difficult.

It is likely that someone is experiencing an anaphylactic reaction if the first two (and probably the third) of these criteria are met:

  1. Sudden onset and rapid progression of symptoms

  2. Life-threatening airway, breathing and/or circulation changes

  3. Skin and/or mucosal changes (such as flushing, itching or swelling)

The patient may also have digestive symptoms, such as abdominal pain, incontinence and vomiting. The person will look and feel unwell and may well be feeling very anxious.

All of these symptoms may also be supported by a history of exposure to a known allergen.

Sudden Onset

One way to tell if an allergic reaction is anaphylactic is how quickly the reaction started. Anaphylactic reactions come on over seconds and minutes rather than 10s of minutes or hours, which might be the case for a severe allergic reaction.

There is a general rule that the speed of onset is related to the severity of the reaction. A very quick onset is likely to have a severe reaction.

Airway Symptoms

The main airway problem is caused by swelling of the throat and tongue. This will cause difficulty breathing and swallowing and may feel like the throat is closing up.

The person may also have a hoarse voice and/or be making a high pitched noise (called stridor) when they breathe in.

Breathing Symptoms

There may also be breathing problems, similar to those in asthma. An increased breathing rate and wheeze (caused by narrowing of the lower airways) may be present. Read the Asthma blog for more details.

These breathing problems may lower the person’s oxygen levels, causing them to become confused and eventually turning their skin a blue colour (cyanosis – a late sign). The person may also become tired due to having to work so hard to breathe. Ultimately, they could go into respiratory arrest which will then lead to cardiac arrest.

Circulation Symptoms

There may also be symptoms of clinical shock. In anaphylactic shock, the person’s blood pressure drops due to their blood vessels relaxing and becoming leaky, and/or due to the heart muscle not working correctly.

This leads to the adrenaline-fuelled ‘fight or flight’ response, characterised by the:

  • Increased breathing and heart rates (to increase blood pressure)

  • Nausea and/or vomiting (as blood is directed away from the digestive system)

  • Pale, cold, clammy skin (as blood is directed away from the peripheral circulation)

If these mechanisms aren't enough to maintain the required blood pressure, eventually the person may become dizzy, confused and pass out.

Ultimately, the person could go in to cardiac arrest. Read the Cardiac Arrest blog for details of what to do in this situation.

Skin and Mucosal Symptoms

These symptoms are present in over 80% of anaphylactic reactions and can be subtle or dramatic. 'Normal' allergic reactions are usually localised - think nettle or insect sting. However, if this reaction gets out of control, symptoms spread around the body, known as a systemic or generalised reaction.

There may be a rash over parts or all of the skin and there may also be raised, red, itchy areas sometimes referred to as hives, nettle rash, weals or welts, often on the chest.

The person may also experience swelling of deeper tissues, commonly around the eyelids, mouth and throat.

Most people who only have skin changes do not go on to develop the life-threatening A, B or C problems that are necessary to signify an anaphylactic reaction.


If you suspect someone is having an anaphylactic reaction, then you need to act quickly as it could rapidly progress and become life-threatening.

  1. Call 999

  2. Remove any trigger such as a sting (but don’t make them sick if they have reacted to something they’ve eaten)

  3. Help the casualty to use their adrenaline auto-injector (AAI) if they have one

  4. If they have breathing problems, help the casualty to use their asthma inhaler (if they have one)

  5. Place them in a comfortable position. Sitting up may help if they have breathing problems, but lie them down and raise their legs if they appear shocked

  6. If symptoms are not getting better or are getting worse, help them to use their second AAI after 5 minutes, if they have one

Using an AAI

There is some evidence that up to 80% of anaphylactic reactions may successfully resolve without the use of an adrenaline autoinjector.

However, as it's difficult to predict who this will apply to, the immediate use of an AAI is still the recommended treatment.

An early dose of adrenaline can be critical in an anaphylactic reaction

Adrenaline works to reverse all of the potential A, B and C problems whilst having very few drawbacks.

There are 3 brands of AAI licensed for use in the UK, most notably Epipen. They are all used in a similar way and have simple instructions written on them. All 3 brands have pens for both adult and paediatric doses.

Click this link to see how to use Emerade

Click this link to see how to use Jext

Click this link to see how to use Epipen

If the person does not have an AAI, take advice from the 999 call handler on what to do.

Under specific legislation, schools may hold a spare AAI that is not prescribed to a particular child. Spare pens are only to be used on a child who has a pen but it is not available. They are not for use in other children who have not been prescribed an AAI.


Whilst anaphylaxis is a potentially life-threatening problem, it is easily treated with adrenaline and is rarely fatal.

Stay calm, call 999 and help the person to take their adrenaline auto-injector if they have one.

Please explore the website and get in touch if you'd like to discuss organising a first aid course.



Clinical Guideline CG134 – Anaphylaxis: Assessment and referral after emergency treatment, NICE, Nov 2016

Emergency Treatment of Anaphylactic Reactions, Resuscitation Council (UK), 2016

Anaphylaxis Campaign, www.anaphylaxis.org.uk