FD&C Blue No. 2: The “Royal Blue” Indigo Dye

FD&C Blue No. 2 is a synthetic food colorant known for its deep, “Royal Blue” hue. While it is a staple in the food industry, it is distinct from FD&C Blue No. 1, which provides a brighter, greenish-blue tint.

Quick Facts: Blue No. 2 at a Glance

Attribute	Detail
Common Names	Indigotine, Indigo Carmine, Acid Blue 74
Hue	Dark/Royal Blue
Solubility	Low in water; soluble in ethanol
Origin	A derivative of indigo made via sulfonation

Attribute	Detail
Common Names	Indigotine, Indigo Carmine, Acid Blue 74
Hue	Dark/Royal Blue
Solubility	Low in water; soluble in ethanol
Origin	A derivative of indigo made via sulfonation

History and Manufacturing

Blue No. 2 holds a significant place in food history as one of the seven original dyes permitted by the Food and Drug Act of 1906.

Unlike many modern synthetic dyes, it is a derivative of indigo. It is manufactured by heating indigo (or indigo paste) in the presence of sulfuric acid and then undergoing a purification process. It was permanently listed for food use in the United States in 1987.

Common Food Uses

You will typically find this colorant used to provide deep blue tones in:

Baked goods and cereals
Snacks and candies
Ice cream

🎨 The Complete Guide to Food Coloring Safety

This article is part of my comprehensive series on synthetic food dyes and their impact on health and regulation.

Main Overview: Why Do They Put Synthetic Colors in Foods?

Related Guides: Blue No. 1, Yellow No. 6, Red No. 40, and Green No. 3.

Safety and the “Tumor” Myth

There is often public concern regarding food dyes, but Blue No. 2 has undergone extensive testing:

No Toxicity: It has not been shown to have toxic or mutagenic effects, even at high feeding levels.
The “Tumor” Myth: While some older reports mentioned tumors in lab rats, these were specifically injection-site tumors and are not associated with ingesting the dye.
Absorption: Like many similar dyes, it is poorly absorbed by the gut.
Daily Intake: The Acceptable Daily Intake (ADI) is set at $2.5 mg/kg, yet actual daily consumption is typically thousands of times less than this limit.