Anaphylaxis is a severe, potentially life-threatening allergic reaction that can develop rapidly.

It is also known as anaphylactic shock.

Signs of anaphylaxis include:

  • itchy skin or a raised, red skin rash
  • swollen eyes, lips, hands and feet
  • feeling lightheaded or faint
  • narrowing of the airways which can cause wheezing and breathing difficulties
  • abdominal pain, nausea and vomiting
  • collapse and unconsciousness

Read more about the symptoms of anaphylaxis.

What to do

Anaphylaxis should always be treated as a medical emergency.

If you suspect that you or somebody else is experiencing symptoms of anaphylaxis, you should immediately dial 999 for an ambulance.

If available, an injection of a medicine called adrenaline should be given if someone is having breathing difficulties, feeling faint, or has lost consciousness due to suspected anaphylaxis.

Some people with a previous history of anaphylaxis will have an auto-injector of adrenaline. This should be injected into their thigh muscle and held in place for 10 seconds. Instructions for how to use these auto-injectors can be found on the side of each device. 

If the person is conscious, you should place them in a position where they are comfortable and able to breathe easily until the ambulance arrives. If they are feeling faint, they should be laid flat with their legs elevated, if possible.

If the person is unconscious, you should place them in the recovery position (on their side, supported by one leg and one arm, with the head tilted back and the chin lifted).

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

Further treatment and observation will be carried out in hospital.

Read more about treating anaphylaxis.

Causes and triggers

Anaphylaxis is the result of your body's immune system overreacting to a harmless substance, such as food. Substances that provoke allergic reactions are known as allergens.

Anaphylaxis usually develops within minutes of contact with an allergen, though sometimes the reaction can happen hours later.

The most widely reported triggers of anaphylaxis are:

  • insect stings, particularly wasp and bee stings
  • nuts
  • other types of foods, such as milk and seafood
  • certain medications, such as some types of antibiotics

Read more about the causes of anaphylaxis.

Preventing further episodes

If you know what has triggered anaphylaxis, it is important to take steps to try to avoid further exposure to similar triggers.

If the cause of the allergic reaction is not known, you should be referred to a specialist allergy clinic where tests can be carried out to help identify possible triggers.

You may be provided with an adrenaline auto-injector to use during any future episodes of anaphylaxis.

Read more about preventing anaphylaxis.

Peanuts are a common trigger for anaphylaxis 

Who is affected?

Anaphylaxis is relatively uncommon, but can affect people of all ages.

People with other allergic conditions, such as asthma or the allergic skin condition atopic eczema, are most at risk of developing anaphylaxis.

Although the condition is life-threatening, deaths are rare. It is estimated that around 20-30 deaths due to anaphylaxis occur in the UK each year. With prompt and proper treatment, most people make a full recovery.


Advice on allergies such as eczema and food allergy, and what treatments are available on the NHS

Page last reviewed: 19/12/2012

Next review due: 19/12/2014