What is anaphylaxis?
Anaphylaxis (pronounced ana-fill-ax-is) is a severe and potentially life-threatening allergic reaction affecting more than one body system such as the airways, heart, circulation, gut and skin. Symptoms can start within seconds or minutes of exposure to the food or substance you are allergic to and usually will progress rapidly. On rare occasions there may be a delay in the onset of a few hours.
What are the causes of anaphylaxis?
The common causes of anaphylaxis include foods such as peanuts, tree nuts, milk, eggs, shellfish, fish, sesame seeds and kiwi fruit, although many other foods have been known to trigger anaphylaxis. Non-food causes include wasp or bee stings, natural latex (rubber), and certain drugs such as penicillin. In some people exercise can trigger a severe reaction – either on its own or in combination with other factors such as food or drugs (e.g. aspirin).
What are the symptoms of anaphylaxis?
You may notice any of these severe symptoms:
There may be a dramatic fall in blood pressure (anaphylactic shock). The person may become weak and floppy and may have a sense of something terrible happening. This may lead to collapse, unconsciousness and – on rare occasions – death.
In addition to those severe symptoms listed above, there may also be:
- Widespread flushing of the skin
- Nettle rash (otherwise known as hives or urticaria)
- Swelling of the skin (known as angioedema) anywhere on the body.
- Swelling of the lips
- Abdominal pain, nausea and vomiting
These symptoms can also occur on their own, without the more severe ones. Where that is the case, the reaction is likely to be less serious but you should watch carefully in case any of the more severe ones develop.
There are several different types of reaction which could occur:
- Uniphasic – these come on quickly and symptoms get rapidly worse, but once treated, the symptoms go and don’t return.
- Bi-phasic – these are reactions which may be mild or severe to start with, followed by a period of time when there are no symptoms, and then increasing symptoms with breathing and blood-pressure problems.
If you have an anaphylactic reaction, you will need an observation period in hospital after you have recovered in case you experience a biphasic reaction. Most biphasic reactions occur within hours of the initial reaction but rarely they can be more delayed (Lee et al, 2015). On very rare occasions, a biphasic reaction has been known to occur as long as 72 hours after the initial reaction.
The length of the observation period would be for your treating doctor to decide. The National Institute for Health and Care Excellence (NICE) recommends that people who have had a severe allergic reaction should be monitored for 6 – 12 hours within a hospital setting because of the risk of a bi-phasic reaction. Children are likely to be admitted to hospital at least overnight (NICE 2011).
- Protracted anaphylaxis – this can last for several days and may need treatment in hospital for some time.
Watch Professor John Warner OBE, a member of our Clinical & Scientific Panel, explain anaphylaxis and allergy:
What is the treatment for a severe reaction?
Pre-loaded auto-injectors (sometimes referred to as ‘pens’) containing adrenaline are prescribed for people believed to be at risk of anaphylaxis. Adrenaline is referred to in some countries as epinephrine, which is the internationally recognised term for adrenaline.
- Find out more about adrenaline auto-injectors
- Our online training programme AllergyWise provides information on what to do in an emergency.
- View our tips on what to do in an emergency.
What increases the risk of a severe reaction?
There are times when you may be particularly vulnerable and at increased risk of a severe reaction. Times when you need to be particularly careful to avoid the culprit allergen include:
- If you have asthma that is poorly controlled
- If you are suffering from an infection, or have recently had one
- If you exercise just before or just after contact with the allergen
- If you are also suffering from aeroallergen symptoms, such as hay fever
- During times of emotional stress
- If you have been drinking alcohol
All the information we produce is evidence based or follows expert opinion and is checked by our expert clinical and research reviewers. If you wish to know the sources we used in producing any of our information products, please let us know, and we will gladly supply details.
Revised March 2017
Review date Oct 2019