What is BLUE #2?

What is BLUE #2?

Blue No. 2 commonly called indigotine, is a synthetic food dye. It was originally discovered in sea snails excriment.

Where does BLUE #2 come from?

Originally extracted the natural dye from several species of plant as well as Phoenician sea snails excriment, but nearly all indigo produced today is synthetic.

How is BLUE #2 made?

A variety of plants, including woad, have provided indigo throughout history, but most natural indigo is obtained from those in the genus Indigofera, which are native to the tropics. In temperate climates indigo can also be obtained from woad (Isatis tinctoria) and dyer's knotweed (Polygonum tinctorum), although the Indigofera species yield more dye. The primary commercial indigo species in Asia was true indigo (Indigofera tinctoria, also known as Indigofera sumatrana). In Central and South America the two species Indigofera suffruticosa (Anil) and Indigofera arrecta (Natal indigo) were the most important.

Is BLUE #2 healty for me?

The FDA says the following about Blue No 2.

Title 21: Food and Drugs
Subpart A—Foods

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§ 74.102   FD&C Blue No. 2.

(a) Identity. (1) The color additive FD&C Blue No. 2 is principally the disodium salt of 2-(1,3-dihydro-3-oxo-5-sulfo-2 H -indol-2-ylidene)-2,3-dihydro-3-oxo-1 H -indole-5-sulfonic acid (CAS Reg. No. 860–22–0) with smaller amounts of the disodium salt of 2-(1,3-dihydro-3-oxo-7-sulfo-2 H -indol-2-ylidene)-2,3-dihydro-3-oxo-1 H -indole-5-sulfonic acid (CAS Reg. No. 54947–75–0) and the sodium salt of 2-(1,3-dihydro-3-oxo-2 H -indol-2-ylidene)-2,3-dihydro-3-oxo-1 H -indole-5-sulfonic acid (CAS Reg. No. 605–18–5). Additionally, FD&C Blue No. 2 is obtained by heating indigo (or indigo paste) in the presence of sulfuric acid. The color additive is isolated and subjected to purification procedures. The indigo (or indigo paste) used above is manufactured by the fusion of N -phenylglycine (prepared from aniline and formaldehyde) in a molten mixture of sodamide and sodium and potassium hydroxides under ammonia pressure. The indigo is isolated and subjected to purification procedures prior to sulfonation.

(2) Color additive mixtures for food use (including dietary supplements) made with FD&C Blue No. 2 may contain only those diluents that are suitable and that are listed in part 73 of this chapter as safe for use in color additive mixtures for coloring foods.

(b) Specifications. The color additive FD&C Blue No. 2 shall conform to the following specifications and shall be free from impurities other than those named to the extent that such other impurities may be avoided by current good manufacturing practice:

Sum of volatile matter at 135 °C (275 °F) and chlorides and sulfates (calculated as sodium salts), not more than 15 percent.

Water insoluble matter, not more than 0.4 percent.

Isatin-5-sulfonic acid, not more than 0.4 percent.

5-Sulfoanthranilic acid, not more than 0.2 percent.

Disodium salt of 2-(1,3-dihydro-3-oxo-7-sulfo-2 H -indol-2-ylidene)-2,3-dihydro-3-oxo-1 H -indole-5-sulfonic acid, not more than 18 percent.

Sodium salt of 2-(1,3-dihydro-3-oxo-2 H -indol-2-ylidene)-2,3-dihydro-3-oxo-1 H -indole-5-sulfonic acid, not more than 2 percent.

Lead (as Pb), not more than 10 parts per million.

Arsenic (as As), not more than 3 parts per million.

Mercury (as Hg), not more than 1 part per million.

Total color, not less than 85 percent.

(c) Uses and restrictions. The color additive FD&C Blue No. 2 may be safely used for coloring foods (including dietary supplements) generally in amounts consistent with current good manufacturing practice except that it may not be used to color foods for which standards of identity have been promulgated under section 401 of the Federal Food, Drug, and Cosmetic Act unless added color is authorized by such standards.

(d) Labeling. The label of the color additive and any mixtures prepared therefrom intended solely or in part for coloring purposes shall conform to the requirements of §70.25 of this chapter.

(e) Certification. All batches of FD&C Blue No. 2 shall be certified in accordance with regulations in part 80 of this chapter.

[48 FR 5260, Feb. 4, 1983]

More information about BLUE #2.

Among other uses, it is used in the production of denim cloth for blue jeans. The form of indigo used in food is called "indigotine", and is listed in the USA as FD&C Blue No. 2, and in the European Union as E Number: E132.

The chemical compound that constitutes the indigo dye is called indican.  Historically, indigo played an important role in many countries' economies because natural blue dyes are rare.



  1. Stephanie
    Dyes are for hair color, not for foods!! Stop putting junk into our foods.

  2. Marla Esposito
    I jumped on this page of info because a bottle of Vitamins, I just opened had Blue #2 in it. Why do we need artificial color in a vitamin...if the natural color is brown, grey.. whatever.. so be it. I\'m taking a vitamin or eating a food to be \"healthy\"...not to have it look prettier and then cause Cancer. Leave he dye\'s OUT.

  3. Mayhem
    I just found out I'm sensitive to blue #2 and red #3 and need to avoid them. I guess I will find out what food and other products it is in and will be avoiding those things.