Commonly added to tablets and capsules; also used in ice cream, sweets, baked goods, confectionery, biscuits. It is also used diagnostically to check for coloured urine in kidney function tests.

A blue synthetic coal tar dye, normally produced by a synthesis of indoxyl by fusion of sodium phenylglycinate in a mixture of caustic soda and sodamide.

This process was introduced following the discovery of the chemical structure of indigo by the Prussian research chemist J F W Adolf von Baeyer in 1883 and was in regular use by 1890. Very little natural indigo from either Isatis tinctoria or Indigofera has been produced commercially since the turn of the century.

Best avoided by people with allergy reactions as it may cause skin sensitivity, a skin rash similar to nettle rash, itching, high blood pressure and breathing problems.

Not recommended for consumption by children.

Banned in Norway.