Anaphylaxis: severe allergic reactions explained
29 January 2014 Last updated at 17:57 GMT
Anaphylaxis is a severe allergic reaction and can be life-threatening.
It can be triggered by many things from nuts, to bee stings or medication.
Here we look at how to spot anaphylaxis and what to do if it happens.
Images courtesy of the Science Photo Library, Dr Pete Smith and the Anaphylaxis Campaign.
Video journalist: Smitha Mundasad