Causes of Anaphylaxis

Anaphylaxis is caused by a problem with the immune system, which is the body’s natural defence against illness and infection.

In the case of anaphylaxis, your immune system overreacts to a harmless substance and releases a number of different chemicals, such as histamine, to deal with the mistaken threat.


Some of the more common triggers for anaphylaxis are shown below.

Insect stings

Most cases of anaphylaxis are caused by wasp and bee stings, although potentially any insect bite or sting can cause anaphylaxis.

It’s estimated around 1 in 100 people will experience an allergic reaction after a wasp or bee sting, but only a small number of these people will go on to develop severe anaphylaxis.


More than half of all cases of food-related anaphylaxis are caused by peanuts.

Other foods known to trigger anaphylaxis include:

  • Nuts – such as walnuts, cashew nuts, almonds, brazil nuts and hazelnuts
  • Milk
  • Fish and shellfish
  • Eggs
  • Some types of fruit – such as bananas, kiwi fruit, grapes and strawberries


Medicines known to trigger anaphylaxis in a small amount of people include:

  • Antibiotics – particularly penicillin-like antibiotics
  • General anaesthetic – muscle-relaxant medicines used during surgery
  • Non-steroidal anti-inflammatory drugs (NSAIDs) – a type of painkiller that includes ibuprofen and aspirin

People sensitive to these types of medicines will usually develop anaphylaxis as soon as they begin a course of treatment, although they may have safely received them in the past.

The risk of anaphylaxis using these types of medicines is very small, so in most cases the benefits of treatment outweigh the potential risk.

For example, the risk of developing anaphylaxis is around:

  • 1 in 1,480 after taking a NSAID-type painkiller
  • 1 in 5,000 after taking penicillin
  • 1 in 10,000 after being given a general anaesthetic

Contrast agents

Contrast agents are a group of special dyes used in some medical tests to help certain areas of your body show up better on scans such as X-rays.

For example, a contrast agent injected into a blood vessel will help show up any problems in the vessel, such as a blockage, on the X-ray. This is known as angiography.

The risk of developing anaphylaxis after being injected with a contrast agent is thought to be less than 1 in 10,000.

Rubber latex

Less than 1 in 100 people in the population has a natural rubber latex allergy. Healthcare, hair, beauty, catering and motor industry workers are more likely to have a latex allergy.

Those with a history of hayfever, asthma, eczema, and certain medical conditions, like spina bifida, are more likely to be affected.

Idiopathic anaphylaxis

Sometimes, despite extensive testing, no trigger can be found for anaphylaxis, and the cause remains unknown. This is known as idiopathic anaphylaxis.


Source: NHS UK