Health A to Z
Anaphylaxis is a severe and potentially life-threatening reaction to a trigger such as an allergy.
It's also known as anaphylactic shock.
This page covers:
Anaphylaxis usually develops suddenly and gets worse very quickly.
The symptoms include:
There may also be other allergy symptoms, including an itchy, raised rash (hives), feeling or being sick, swelling (angioedema), or stomach pain.
Anaphylaxis is a medical emergency. It can be very serious if not treated quickly.
If someone has symptoms of anaphylaxis, you should:
If you're having an anaphylactic reaction, you can follow these steps yourself if you feel able to.
Read about how to treat anaphylaxis for more advice about using auto-injectors and correct positioning.
Anaphylaxis is the result of the immune system – the body's natural defence system – overreacting to a trigger.
This is often something you're allergic to, but isn't always.
Common anaphylaxis triggers include:
In some cases, there's no obvious trigger. This is known as idiopathic 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:
Read more about how to prevent anaphylaxis.
Anaphylaxis is a medical emergency that requires immediate medical assistance and treatment.
If someone has symptoms of anaphylaxis, you should:
If you're having an anaphylactic reaction, you can follow these steps yourself if you feel able to.
People with potentially serious allergies will often be given an adrenaline auto-injector to carry at all times. This can help stop an anaphylactic reaction becoming life threatening.
This should be used as soon as a serious reaction is suspected, either by the person experiencing anaphylaxis or someone helping them.
If you've been given an auto-injector, make sure you're aware how to use it correctly.
There are three main types of adrenaline auto-injector, which are used in slightly different ways.
These are:
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.
Someone experiencing anaphylaxis should be placed in a comfortable position.
If the person's breathing or heart stops, cardiopulmonary resuscitation (CPR) should be performed immediately.
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:
You should be able to go home when the symptoms are under control and it's thought they won't 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 antihistamine and steroid tablets for a few days after leaving hospital to help stop your symptoms returning.
You will also probably be asked to attend a follow-up appointment with an allergy specialist so you can be given advice about how you can avoid further episodes of anaphylaxis.
An adrenaline auto-injector may be provided for emergency use between leaving hospital and attending the follow-up appointment.
If you have a serious allergy or have experienced anaphylaxis, it's important to try to prevent future episodes.
The main things you can do to reduce your risk are outlined below.
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 haven't 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:
Read more about diagnosing allergies and allergy testing.
If a trigger has been identified, you'll need to take steps to avoid it in the future whenever possible. See below for advice about avoiding some specific triggers.
You can reduce the chances of being exposed to a food allergen by:
Read about living with a food allergy for more information.
You can reduce your risk of being stung by an insect by taking basic precautions, such as:
Some specialist allergy centres can also offer special treatment to help desensitise you to insect stings (immunotherapy).
Read more about preventing insect stings.
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:
Always tell any healthcare professional about medicine allergies you have, as they may not be aware of them.
You may be prescribed an adrenaline auto-injector if there's an ongoing risk you could develop anaphylaxis.
There are three types of auto-injector – EpiPen, Jext and Emerade – that are each slightly different. Click on the links for advice about how to use these injectors.
It's important to remember the following:
If your child has an auto-injector, they will need to change over to an adult dose once they reach 30kg (approximately 4.5 stone).