Anaphylaxis is an extreme allergic response which can be life-threatening.

Those who experience anaphylactic shock require immediate emergency medical attention.

An anaphylactic response happens when the body’s immune response system overreacts to the presence of a trigger substance.

A reaction takes place between the trigger substance and the body’s allergic antibody known as immunoglobulin E (IgE). This releases a sudden rush of chemicals, including histamine, causing a swelling in blood vessels throughout the body.

What are the symptoms of anaphylaxis?

You may experience one, some or all of the below symptoms when you have an anaphylactic reaction:

  • A rapid and/or weak pulse
  • A skin rash
  • Nausea or vomiting
  • Swollen eyes, lips, hands or feet
  • Lightheadedness
  • Difficulty breathing due to swelling in the mouth or airways


There is no single test available to confirm whether or not you are at risk of having an anaphylactic reaction. It is a fairly rare condition but it can happen to anyone at any stage in their life.

There are certain risk factors which could mean you are more likely to experience anaphylaxis.

These include:

  • A history of anaphylactic reaction. If you have had a severe reaction in the past then there is a chance you could have it again.
  • Those who have allergies or asthma.
  • Those with a family history of anaphylaxis.

If you are classed as high risk your GP may carry out some tests to try and determine what your allergy triggers are.

The results will not be able to give an indication of the severity of your reaction or the likelihood of anaphylactic shock, although they may be able to help you make informed choices about what you eat and what you do.

  • Skin tests. The skin is pricked to expose it to a very small amount of various allergens to see how it reacts. An allergen would usually cause the skin to go red and itchy.
  • Blood tests. Blood samples are taken and sent off for analysis which can help to determine how a person reacts to various allergens.
  • A food diary. This is a diary where you keep track of all the foods you eat in order to see if there is a link between them and when you have an allergic reaction.
  • Other conditions. Your doctor or allergy specialist will try to rule out the likelihood that your reaction could be linked to another condition. Conditions that produce similar symptoms can include panic attacks, immune system disorders, heart or lung conditions and seizures.

Anaphylaxis triggers

Anaphylaxis can be caused by numerous triggers.

The most common include:

  • Food. Especially nuts, shellfish, seafood, milk and eggs.
  • Insect stings or bites. From wasps, bees, hornets and ants.
  • Latex. A common material in the manufacture of condoms.
  • Contrast agents. Used intravenously in some x-ray diagnostics.
  • Medicines. Aspirin, ibuprofen and antibiotics.

What is the difference between an anaphylactic shock and an allergic reaction?

When a person who has an allergy comes into contact with one of their triggers their body responds as though it is being attacked and releases chemicals to the specific area.

For example, those living with hay fever may experience itchy eyes or sneezing as pollen particles enter the body via the nose and eyes.

However, in the case of an anaphylactic shock, a reactive chemical known as histamine is released into the bloodstream. This causes a more extensive reaction throughout the body, often noticeable through swollen body parts, a skin rash and breathing problems.

Anaphylaxis is almost always instant but it can also occur a short while after exposure to a trigger source.

How can I prevent an anaphylactic reaction?

Living with a severe allergy can be unpredictable as you cannot always guarantee that you will avoid your triggers.

However, that being said, you should do whatever you can to try and limit your contact.

  • Know your trigger.

You need to know what triggers your reaction so that you can make a plan on how to avoid it as much as possible. Your doctor will be able to tell you the best way to do this.

  • Alert others.

Once you know what your allergen is you should inform those closest to you so that they can help you to avoid it. Some people find it helpful to wear a bracelet or necklace which holds the details of their allergies.

  • Be cautious.

You should always use caution when it comes to your triggers.

If you are allergic to wasps and bees, be prepared when outdoors during warmer weather. You might want to adapt your clothing so that the colours you wear are not too bright and you have less skin on display.

Those with food allergies should carefully read labels and when eating out and speak to restaurant staff before ordering dishes.

How is anaphylaxis treated?

The majority of anaphylactic reactions can be treated successfully. The Resuscitation Council (UK) states that less than one percent of incidents result in fatality.

If you have an anaphylactic shock you can expect to be treated with the following:

  • Adrenaline (also called epinephrine) is very important in the treatment of the condition.

It can be administered immediately when anaphylactic symptoms are observed. A standard dose is usually delivered via an intramuscular autoinjector device also known as an EpiPen.

  • Oxygen.

The body may be lacking in oxygen while the airways are constricted. Therefore a high concentration delivered directly into the airways can help to alleviate symptoms.

  • Intravenous drugs.

Following on from initial adrenaline treatment you may be given antihistamines and corticosteroids intravenously. These two types of drugs can counteract blood vessel dilation and airway constriction, and also reduce the length of the reaction or the likelihood that a secondary reaction will follow.

Page last reviewed:  01/10/2020