Anaphylaxis and Severe Allergic Reactions

If you are experiencing a serious reaction or anaphylaxis, call 999 immediately.

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Anaphylaxis is a life threatening severe allergic reaction. It is a medical emergency and requires immediate treatment. A severe allergic reaction can cause an anaphylactic shock and must be treated with an Adrenaline Auto-Injector (AAI).

This page provides the most up-to-date guidance on anaphylaxis and AAIs.  Knowing how to recognise the early signs of anaphylaxis and administer AAI’s can save a life.

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Symptoms of anaphylaxis – The ABCs

Knowing how to recognize the symptoms of anaphylaxis can provide individuals and their caregivers with peace of mind, empowering them to navigate their allergy management confidently. Anaphylaxis can occur rapidly and escalate quickly, making it essential to recognise the signs and symptoms early on.

Signs of a severe allergic reaction (anaphylaxis) include one or more of the following symptoms:


  • Swollen tongue, difficulty swallowing, throat tightness, change in voice (hoarse/croaky)


  • Difficulty breathing, chest tightness, noisy breathing, persistent cough, wheeze,


  • Feeling dizzy or faint, collapse, loss of consciousness, pale and floppy (in babies/small children)

What causes an anaphylactic reaction?

In most allergic reactions the resulting chemicals are released locally into the tissues in a particular part of the body (skin, eyes etc.). This means the symptoms of the allergic reaction usually only occur in this area.

In anaphylaxis, the chemicals that cause the allergic symptoms (e.g. histamine) are released into the bloodstream. The symptoms of anaphylaxis usually occur within minutes of exposure to the trigger substance (allergen) but sometimes an hour or so later.

The most common causes of anaphylactic reactions include:

  • Foods – including nuts, milk, fish, shellfish, eggs and some fruits
  • Medicines and drugs – including some antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) like aspirin
  • Insect stings – particularly wasp and bee stings
  • General anaesthetic
  • Contrast agents – dyes used in some medical tests to help certain areas of your body show up better on scans
  • Latex – a type of rubber found in some rubber gloves and condoms.

In some cases, there’s no obvious trigger. This is known as idiopathic anaphylaxis.

Anaphylaxis and severe allergic reactions

Download our information factsheet to learn more about what anaphylaxis is, including its causes, triggers, and prevalence. Understand why prompt recognition and treatment are vital for managing this serious condition.

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Anaphylaxis symptoms and action sheet

Our Anaphylaxis Symptoms and Action Sheet is your essential resource for recognising the signs of anaphylaxis and knowing how to respond swiftly and effectively in case of an emergency. Download your copy today and empower yourself with life-saving knowledge.

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Adrenaline auto-injectors

Adrenaline auto-injectors (AAI’s) are devices designed to deliver a dose of adrenaline quickly and easily in case of a severe allergic reaction, such as anaphylaxis. These devices are compact, portable, and typically come in a pen-like form, making them convenient to carry and use during emergencies.

Adrenaline auto-injectors work by injecting a pre-measured dose of adrenaline into the thigh muscle, to counteract the effect of an allergic reaction. Adrenaline acts rapidly to constrict blood vessels, relax muscles in the airways, and increase heart rate, helping to alleviate symptoms and stabilise the individual until further medical help can be obtained.

It’s essential for individuals with severe allergies, as well as their caregivers, to know how to use AAI’s correctly. Training and education on proper administration techniques are crucial to ensure prompt and effective treatment during emergencies.

Carry adrenaline auto-injectors

You may be prescribed an adrenaline auto-injector if there’s an ongoing risk you could develop anaphylaxis.

There are two types of auto-injectors – EpiPen and Jext – that are each slightly different. Instructions are also included on the side of each injector if you forget how to use it or someone else needs to give you the injection.

It’s important to remember the following:

  • Carry 2 in-date auto-injectors at all times. There should be no exceptions; you may also be advised to get an emergency card or bracelet with full details of your allergy and doctor’s contact details to alert others
  • Make sure you and any carers know when and how to use your auto-injector – read the leaflet that comes with it and practise with a training device, which you can get from the manufacturer
  • Extremes of heat can make adrenaline less effective, so do not leave your auto-injector in the fridge or your car’s glove compartment, for example
  • Check the expiry date regularly and replace it before it expires. An out-of-date injector will offer limited protection
  • Manufacturers offer a reminder service, where you can be contacted near the expiry date – check the information leaflet that comes with your medicine for more information
  • Do not delay injecting yourself if you think you may be experiencing anaphylaxis, even if your initial symptoms are mild – it’s better to use adrenaline early and then find out it was a false alarm than delay treatment until you’re sure you’re experiencing severe anaphylaxis.
Adrenaline auto-injectors

Adrenaline auto-injectors

This information factsheet has been developed to highlight the importance of carrying your adrenaline auto-injectors. It will also cover the different types and brands of adrenaline auto injectors available in the UK as well as how to care for your adrenaline auto injector.

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Preventing anaphylaxis

If you have a serious allergy or have experienced anaphylaxis before, it’s important to try to prevent future episodes.

The following can help reduce your risk:

Identify triggers

Finding out if you’re allergic to anything that could trigger anaphylaxis can help you avoid these triggers in the future.

If you’ve had anaphylaxis and have not already been diagnosed with an allergy, you should be referred to an allergy clinic for tests to identify any triggers.

The most commonly used tests are:

  • Skin prick test – your skin is pricked with a tiny amount of a suspected allergen to see if it reacts
  • Blood test – a sample of your blood is taken to test its reaction to a suspected allergen

Avoid triggers

If a trigger has been identified, you’ll need to take steps to avoid it in the future whenever possible.


You can reduce the chances of being exposed to a food allergen by:

  • Checking food labels and ingredients
  • Letting staff at a restaurant know what you’re allergic to so it’s not included in your meal. Allergy UK’s translation cards for eating out when travelling abroad are available via our Helpline.
  • Remembering some types of food may contain small traces of potential allergens – for example, some sauces contain wheat and peanuts
  • Identify any triggers – you may be referred to an allergy clinic for allergy tests to check for anything that could trigger anaphylaxis
  • Avoid triggers whenever possible – for example, be careful when food shopping or eating out if you have a food allergy
  • Carry two in-date adrenaline auto-injectors at all times – give yourself an injection whenever you think you may be experiencing anaphylaxis, even if you’re not completely sure

Insect stings

You can reduce your risk of being stung by an insect by taking basic precautions, such as:

  • Moving away from wasps, hornets or bees slowly without panicking – do not wave your arms around or swat at them
  • Using an insect repellent if you spend time outdoors, particularly in the summer
  • Being careful drinking out of cans when there are insects around – insects may fly or crawl inside the can and sting you in the mouth when you take a drink
  • Not walking around outside with bare feet

Some specialist allergy centres can also offer special treatment to help desensitise you to insect stings (immunotherapy).

Drugs and medicines

If you’re allergic to certain types of medicines, there are normally alternatives that can be safely used.

For example, if you’re allergic to:

  • Penicillin – you can normally safely take a different group of antibiotics known as macrolides.
  • Non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and aspirin – you can normally safely take paracetamol; read the ingredients of things like colds medicines carefully to make sure they do not contain NSAIDs
  • One type of general anaesthetic – others are available, or it may be possible to perform surgery using a local anaesthetic or an epidural injection.

Always tell any healthcare professional about medicine allergies you have, as they may not be aware of them.

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Positioning and resuscitation

Someone experiencing anaphylaxis should be placed in the correct position:

  • Most people should lie flat with their legs raised
  • If they’re pregnant they should lie on their left side
  • People having trouble breathing should sit up for a short time to help make breathing easier, and then lie down again when possible
  • Avoid a sudden change to an upright posture such as standing or sitting up – this can cause a dangerous fall in blood pressure

If the person’s breathing or heart stops, cardiopulmonary resuscitation (CPR) should be performed immediately.

In hospital

You will need to go to hospital for observation – usually for 6-12 hours – as the symptoms can occasionally return during this period.

While in hospital:

  • An oxygen mask may be used to help breathing
  • Fluids may be given directly into a vein to help increase blood pressure
  • Additional medicines such as antihistamines and steroids may be used to help relieve symptoms
  • Blood tests may be carried out to confirm anaphylaxis

You should be able to go home when the symptoms are under control and it’s thought they will not return quickly. This will usually be after a few hours, but may be longer if the reaction was severe.

You may be asked to take antihistamines and steroid tablets for a few days after leaving hospital to help stop your symptoms returning.

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