There are some substances that are added to food during the manufacturing process. These substances are not normally consumed as food themselves. Many additives also occur naturally, such as the vitamins (E.g. Vitamin C in fruits and vegetables).
Additives are used in processed food to restore or improve taste, improve or restore appearance, improve and prolong quality and prolong the life-span of the food. They should be listed with their name and a corresponding number. For example citric acid (330), ascorbic acid (300) or preservative (223). Some people (about 5% of the population) have allergic reactions to these additives.
In Australia, these additives and preservatives are rigorously tested. For more information visit the Food Standards Australia and New Zealand (FSANZ) website at http://www.foodstandards.gov.au.