Indigotine
The short version
A synthetic blue dye (indigo carmine) — common in confectionery and ice cream, with documented allergy reports.
A synthetic blue dye (Indigotine / Blue 2). It adds colour only and can occasionally cause allergic-type reactions in sensitive people, which is why we flag it.
Where it comes from
A sulfonated derivative of the ancient natural indigo dye, first synthesized in the 1880s. Industrially produced by sulfonation of indigo (the molecule originally extracted from Indigofera plants and now made synthetically).
How it's used
Used to color sweets, ice creams, soft drinks, baked goods, and pharmaceutical tablets and capsules. Frequently combined with tartrazine (E102) for green shades or with brilliant blue (E133) for deeper blues. Common in pill coatings.
Safety profile
ADI of 5 mg/kg body weight. Considered safer than the Southampton six but documented to cause hypersensitivity reactions (urticaria, bronchospasm) in a small subset of individuals, particularly when injected as a diagnostic dye. Some studies report behavioral effects but evidence is weaker than for azo dyes.
Physical & chemical properties
Dark blue to purple-blue powder, moderately soluble in water. Sensitive to oxidation, heat, and light — among the less stable synthetic food dyes. Fades noticeably in light-exposed products.
Regulation worldwide
Permitted in the EU, US (as FD&C Blue No. 2), and most jurisdictions. No mandatory warning label.
Educational information only. Not medical or dietary advice.