Unlike medicines that help relieve bothersome cold symptoms, First defence nasal spray works at the first signs of a cold by targeting the viruses to help stop the cold in its tracks before the symptoms get worse.nWhen used at the first signs of a cold, First Defence nasal spray acts at the back of the nose directly where the cold virus takes hold and starts to develop(that\'s why it\'s a nasal spray). It traps, inactivates and helps your body naturally remove the cold virus, before it develops into a full blown cold.