Being sensitised means that the immune system has previously been in contact with an allergen, has committed it to ‘memory’, and is ready to launch a defence the moment the allergen reappears.

The time it takes to become sensitised to an allergen varies from person to person (from a few days to several years).

If an individual does come into contact with the same allergen again, there is a huge response by the immune system and the symptoms of allergy are displayed.