NHS website

Anaphylaxis

Find out about the symptoms of anaphylaxis, how to treat it, why it happens and how to prevent it.

3 October 2018

Introduction

Anaphylaxis is a severe and potentially life-threatening reaction to a trigger such as an allergy.

It's also known as anaphylactic shock.

Symptoms of anaphylaxis

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 ↗.

What to do if someone has anaphylaxis

Anaphylaxis is a medical emergency. It can be very serious if not treated quickly.

If someone has symptoms of anaphylaxis, you should:

  1. use an adrenaline auto-injector if the person has one – but make sure you know how to use it correctly first
  2. call 999 for an ambulance immediately (even if they start to feel better) – mention that you think the person has anaphylaxis
  3. remove any trigger if possible – for example, carefully remove any wasp or bee sting stuck in the skin
  4. lie the person down flat – unless they're unconscious, pregnant or having breathing difficulties
  5. give another injection after 5-15 minutes if the symptoms don't improve and a second auto-injector is available

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.

Triggers of anaphylaxis

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.

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 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, you should be careful when food shopping or eating out if you have a food allergy ↗
  • carry your adrenaline auto-injector at all times (if you have two, carry them both) – give yourself an injection whenever you think you may be experiencing anaphylaxis, even if you're not completely sure

Read more about how to prevent anaphylaxis ↗.