What is Anaphylaxis?

What is anaphylaxis?

An allergic reaction is caused by your body’s immune system over-reacting to the presence of a foreign body. It responds to something harmless as if it is a threat. Your body may be so sensitive that tiny quantities of the allergen can cause a reaction.  Your body releases chemical substances, including histamine, from cells in the blood and tissues where they are stored.  This happens when the allergic sort of antibodies (IgE) react with the foreign body (allergen).  The chemicals act on your blood vessels to cause swelling and low blood pressure, and on your lungs to cause asthma. When you have an anaphylactic shock, your blood vessels leak, bronchial tissues swell and blood pressure drops, causing you to choke and collapse.

What causes anaphylactic shock?

The most common causes of anaphylactic shock are:

  • peanuts
  • tree nuts such as almonds, walnuts, cashews, brazil nuts
  • sesame
  • fish
  • shellfish
  • dairy products
  •  eggs
  • soya
  • wasp or bee stings
  • natural latex (rubber)
  • penicillin and other drugs

Severe allergic reactions to fresh fruit, such as kiwis and apples, are increasing.  In some people, exercise can trigger a reaction – either on its own, or combined with other factors such as eating a certain food.  ‘Idiopathic anaphylaxis’ has no obvious trigger.

What are the symptoms?

You may have some or all of the following symptoms:

  • your throat and mouth swell
  • you find it hard to swallow or speak
  • your heart rate changes
  • you find it hard to breathe – due to severe asthma or throat swelling
  • you have hives anywhere on the body, especially large hives
  • your skin is flushed all over
  • stomach cramps, nausea and vomiting
  • you feel sudden weakness (drop in blood pressure)
  • you have a sense of impending doom
  • you collapse or fall unconsciousness

If you have any type of allergic reaction, you should see your GP. Your doctor may refer you on to an allergy specialist.  You should treat it as very serious if you find it hard to breathe or swallow or have a sudden weakness or floppiness.
How is it treated?

You can reverse an anaphylactic reaction with an injection of adrenaline (also called epinephrine).  Adrenaline acts quickly to constrict blood vessels, relax your lungs to improve breathing, stimulate your heartbeat and help to stop swelling around your face and lips.  This swelling is called angioedema. If you have a serious reaction, the normal medical treatment is an immediate injection of adrenaline.  If you do not improve in five minutes, you will need a second injection.  Every time you have a serious reaction, you should receive adrenaline and call an ambulance. You will need to go to hospital for more medical treatment and observation.  This is important, because the reaction may happen again some time later. Because an anaphylactic reaction can be fatal, you must get clear guidance from your doctor about how and when to inject adrenaline.  You should know the range of symptoms so you can tell when a reaction is serious.


You can get easy-to-use pre-loaded injector pens for injecting adrenaline. In Ireland, the best known are the Anapen, the Jext and the Epi-pen.  You can get these on prescription from your local pharmacy.

The information in this site should not be considered in any way whatsoever as medical advice or opinion. Readers must consult with their own doctor to deal directly with their specific circumstances. Products mentioned are not endorsed and are referred to solely as a matter of convenience to the reader.