Anaphylaxis occurs when the body's immune system, or natural defence system, overreacts to a trigger allergen.
This is often something you are frequently allergic to, but this is not always the case.
The following are common anaphylactic triggers:
Foods - nuts, eggs, fish
Medication - antibiotics, non-steroidal anti-inflammatory drugs (NSAIDs) e.g. Aspirin
Insect bites or stings - bees, wasps, ants
General anaesthetic drugs
Contrast agents (dyes) - used in medical tests or scans
Latex - rubber gloves, condoms
In as many as 1 in 4 cases of anaphylaxis, no trigger can be identified despite extensive testing. This is known as Idiopathic Anaphylaxis.