Green S is a green synthetic coal tar

Coal tar

Coal tar is a brown or black liquid of extremely high viscosity, which smells of naphthalene and aromatic hydrocarbons. Coal tar is among the by-products when coal iscarbonized to make coke or gasified to make coal gas...

 triarylmethane dye

Dye

A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....

 with the molecular formula C₂₇H₂₅N₂O₇S₂Na.

As a food dye, it has E number

E number

E numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...

 E142. It can be used in mint sauce

Mint Sauce

Mint sauce is a sauce traditionally made from finely chopped spearmint leaves, soaked in vinegar, and a small amount of sugar. Occasionally, the juice from a squeezed lime is added. The sauce should have the consistency of double cream...

, dessert

Dessert

In cultures around the world, dessert is a course that typically comes at the end of a meal, usually consisting of sweet food. The word comes from the French language as dessert and this from Old French desservir, "to clear the table" and "to serve." Common Western desserts include cakes, biscuits,...

s, gravy

Gravy

Gravy is a sauce made often from the juices that run naturally from meat or vegetables during cooking. In North America the term can refer to a wider variety of sauces and gravy is often thicker than in Britain...

 granules, sweets

SweetS

was a Japanese idol group. Put together through auditions, the group debuted in 2003 on the avex trax label. Although the group met minor success, they disbanded after three years with the release of a final single in June 2006....

, ice cream

Ice cream

Ice cream is a frozen dessert usually made from dairy products, such as milk and cream, and often combined with fruits or other ingredients and flavours. Most varieties contain sugar, although some are made with other sweeteners...

s, and tinned pea

Pea

A pea is most commonly the small spherical seed or the seed-pod of the pod fruit Pisum sativum. Each pod contains several peas. Peapods are botanically a fruit, since they contain seeds developed from the ovary of a flower. However, peas are considered to be a vegetable in cooking...

s. Green S is prohibited as a food additive in Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, and Norway

Norway

Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

. It is approved for use as a food additive

Food additive

Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...

 in the EU and Australia and New Zealand.
Green S is a vital dye, meaning it can be used to stain

Staining (biology)

Staining is an auxiliary technique used in microscopy to enhance contrast in the microscopic image. Stains and dyes are frequently used in biology and medicine to highlight structures in biological tissues for viewing, often with the aid of different microscopes...

 living cells

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

. It is used in ophthalmology

Ophthalmology

Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...

, among fluorescein

Fluorescein

Fluorescein is a synthetic organic compound available as a dark orange/red powder soluble in water and alcohol. It is widely used as a fluorescent tracer for many applications....

 and rose bengal

Rose bengal

Rose Bengal is a stain. Its sodium salt is commonly used in eye drops to stain damaged conjunctival and corneal cells and thereby identify damage to the eye...

, to diagnose various disorders of the eye's surface.

Green S may cause allergic reactions and is one of the colorants that the Hyperactive Children's Support Group recommends to be eliminated from the diet of children.