A food additive may be regarded as a substance, either synthetic or natural, which is normally not consumed as food itself, but is deliberately added, usually in small amounts. The substance is intended to remain in food for some desirable function or effect during manufacturing, production, processing, storage or packaging or in the finished product. Food additives enhance the appearance, quality, consumer acceptability and flavour of foods, extend shelf-life and allow mass production, mass distribution and ready availability. They may facilitate and standardise preparation, enhance nutritional value or provide for specific dietary requirements. Azo dyes are colour-fast and are commonly used as colouring agents.

Food additives, e.g. salts and spices have been used throughout recorded food history. Nutrients of various types have been added to food to minimise the incidence of conditions, known to be due to deficiency, in the community diet. Iodine, calcium and more controversially fluoride have been added to food.

The functions of nutritional additives include enrichment and fortification. Enrichment replaces nutrients lost during processing through oxidation or reaction with food components, e.g. ascorbic acid and thiamin, which are lost through chemical and enzymatic degradation. Fortification is the addition during manufacture of substances to improve dietary intake, e.g. vitamins in margarine.

A distinction has to be made between toxic substances and a toxic effect. All substances have the potential to be toxic, but only at a concentration at which the substance produces that toxic effect. The use of food additives free from toxic effects is controlled by regulatory and advisory committees within the European Union Commission, the United States Food and Drugs Administration and the World Health Organisation. The decisions of these policy-making bodies are based upon scientific studies (e.g. toxicity studies), which include evidence of safety to the foetus and absence of the potential to cause cancerous changes in cells. . There are, however, inevitable tensions between regulations and the need to produce food economically. None the less, all additive manufacturers must follow the stipulated guidelines and demonstrate both the safety and need for their product.

The guidelines also identify a Acceptable Daily Intake ( ADI) which is an estimate of the amount of the food additive expressed on a body weight basis that can be ingested daily over a life time without appreciable health risk and is expressed on a milligram /kilogram body weight basis ( mg/ kgbw /day). This is a widely used measurement and is applicable to people of all ages. Some additives come into the category of Generally Regarded as Safe ( GRAS), for example, ascorbic acid .

There are also negative effects of food additives. Anti-oxidants, spices, gums and waxes may result in dermatitis. Tartrazine, the anti-oxidants BHA and BHT and sacramen may cause urticaria. There is an increased risk of tartrazine sensitivity in aspirin-intolerant patients. Benzoic acid and sodium benzoate, which are used to suppress the growth of yeast and bacteria in food, can cause skin and asthmatic reactions, particularly in patients already suffering from asthma. Sodium monoglutamate can produce the ‘Chinese restaurant syndrome’, bronchospasm, flushing and headache.