Anaphylactic Shock

Useful links – The Anaphylaxis Campaign

What is an allergic reaction?

All allergic reactions occur because the body’s immune system reacts inappropriately in response to the presence of a substance that it wrongly perceives as a threat.

An acute allergic, or anaphylactic, reaction is caused by the sudden release of chemical substances, including histamine, from cells in the blood and tissues where they are stored. The release is triggered by the reaction between the allergic antibody (IgE) and the substance (allergen) causing the anaphylactic reaction. This mechanism is so sensitive that minute quantities of the allergen can cause a reaction. The released chemicals act on blood vessels to cause the swelling in the mouth and anywhere on the skin. There is a fall in blood pressure and in asthmatics the effect may be mainly on the lungs, causing a severe asthma attack which their inhaler is unable to help.

We have small amounts of histamine in our system normally and it is important for various vital functions of the body including regulating stomach acid and as a neurotransmitter in our nerve cells. However larger amounts of histamine being released leads to symptoms such as sneezing, blocked nose, itching… the sort of symptoms often associated with hayfever. Antihistamine medication can work effectively at resolving these symptoms. Antihistamine medication typically takes around 15 minutes to work.

Life threatening and systemic allergic reactions are caused by the body producing even more histamine, which dilates small blood vessels and causes them to leak, resulting in swelling in areas such as the lungs – leading to breathing problems. Sufferers may have a rash and be flushed due to the increased blood supply to the skin. Their blood pressure drops and they may collapse.

Allergic reaction

Picture thanks to the Anaphylaxis Campaign

Who is at risk from anaphylaxis?

If a patient has suffered a bad allergic reaction in the past – whatever the cause, this may make them more prone to having further severe reactions. If a significant reaction to a tiny dose occurs, or a reaction has occurred with just skin contact, this could indicate that they are sensitive to this particular thing and greater contact could lead to a more severe attack.  Asthma can put a patient in a higher risk category.

Common triggers for reactions

Individuals can react to absolutely anything and in some people, exercise can trigger a severe reaction – either on its own or in combination with other factors such as food or drugs (e.g. aspirin).

However most common causes include foods: such as peanuts, tree nuts (e.g. almonds, walnuts, cashews, and Brazil nuts), sesame, fish, shellfish, dairy products and eggs.

Non-food causes include wasp or bee stings, natural latex (rubber), penicillin or any other drug or injection.

How to recognise an acute allergic reaction?

A reaction can take any form and people who have reacted one way when exposed to a particular allergen can react completely differently on another occasion when exposed to the same thing. It is therefore extremely difficult to predict what a reaction might look like. The above picture is a very classic reaction and easily recognisable as Anaphylactic shock.

Common symptoms include:

Generalised flushing of the skin

A rash or hives anywhere on the body

A feeling of anxiety or ‘sense of impending doom’

Swelling of throat and mouth and difficulty in swallowing or speaking

Alterations in heart rate – usually a speeding up of the heart

Severe asthma attack which isn’t relieved by their inhaler

Acute abdominal pain, violent nausea and vomiting

A sudden feeling of weakness followed by collapse and unconsciousness

A patient is unlikely to experience all of the above symptoms.

How to Treat Anaphylaxis

The key advice is to avoid any known allergens if you are able to.

Adrenaline auto-injectors are prescribed for those believed to be at risk. Adrenaline (also known as epinephrine) acts quickly to constrict blood vessels, relax smooth muscles in the lungs to improve breathing, stimulate the heartbeat and help to stop swelling around the face and lips.

Acute Allergic reactions can be life threatening and it is crucially important that you recognise the problem and know what to do quickly in order to save someone’s life.


Adrenaline ( US name: Epinephrine) is the first choice for an acute anaphylactic reaction and it works best if it is given as soon as you recognise that someone is having a reaction. You should administer the injector, or help the sufferer to administer it themselves, as quickly as possible and call for an ambulance stating clearly that the person is having an acute anaphylactic reaction.

Adrenaline rapidly treats all of the most dangerous symptoms of anaphylaxis, including throat swelling, difficulty breathing, and low blood pressure.






There are currently 2 makes of Adrenaline Autoinjectors on the market in the UK; Epipen  and Jext. Epipen is by far the most popular in the UK.

Some people may have an Anapen, you activate the device by pressing the red button (videos as to how to use this device are widely available on-line.) This device has never been widely used in the UK and was withdrawn in September 2012.

Jext has recently launched. This is very similar in design and delivery to the Epipen and may well become a more popular option as it has a longer shelf life of 2 years.

If you are prescribed an auto injector you should carry it with you at all times and register it to receive a reminder when it is going out of date. If you have been prescribed 2 injectors as a duo pack, you need to carry both with you at all times in case a second dose is needed. Teach friends and family what to do if they need to help you or someone else having an anaphylactic reaction.

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