Anaphylaxis is a severe and potentially life-threatening allergic reaction. Anaphylaxis is a medical emergency. It can be very serious if not treated quickly. If someone has symptoms of anaphylaxis (see below), you should call 999 for an ambulance immediately.

Symptoms of anaphylaxis

Anaphylaxis usually develops suddenly and gets worse very quickly. It's also known as anaphylactic shock.

The symptoms include:

  • feeling lightheaded or faint
  • difficulty breathing – such as choking due to throat / tongue swelling, shortness of breath or wheezing
  • an itchy, raised rash (hives) - rash is not always present (present in about 80 per cent of cases)
  • a fast heartbeat
  • clammy skin
  • confusion and anxiety
  • collapsing or losing consciousness

There may also be other symptoms, including feeling or being sick, swelling (angioedema) for example at the site of a sting, 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:

  • call 999 for an ambulance immediately – mention that you think the person has anaphylaxis - it is important to have help on the way
  • remove any trigger if possible – for example, carefully remove any wasp or bee sting stuck in the skin
  • lie the person down flat – unless they're unconscious, pregnant or having difficulty breathing - people having difficulty breathing are more comfortable sitting
  • If they are unconscious, make sure that they are breathing and have a pulse. If in doubt start CPR (chest compressions and life support). If unconscious and breathing, place them in the recovery position
  • use an adrenaline auto-injector if the person has one – but make sure you know how to use it correctly first
  • 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.

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:

  • foods – including nuts, milk, fish, shellfish, eggs and some fruits
  • medicines – including some antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin
  • insect stings – particularly wasp and bee stings
  • general anaesthetic
  • contrast agents – special 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.

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 – give yourself an injection whenever you think you may be experiencing anaphylaxis, even if you're not completely sure


The information on this page has been adapted from original content from the NHS website.

For further information see terms and conditions.

This page was published December 2017

This page is due for review March 2020

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