Blue 2
A synthetic blue color additive (also called indigotine or indigo carmine) used to make foods look uniformly blue or to blend with other dyes for greens and purples.
Should I eat Blue 2?
Blue 2 is a synthetic color that adds no nutrition but is considered safe for most people at typical intakes under strict impurity controls. If you want to minimize artificial dyes—especially for kids—choose dye‑free or naturally colored products.
Summary
Blue 2 (indigotine/E132) is widely authorized and tightly regulated, with FDA batch certification and international impurity limits. EFSA and JECFA set an ADI of 0–5 mg/kg body weight/day and found no genotoxicity concerns at permitted uses. Modeling shows some high‑consuming children could exceed the ADI if foods are colored at maximum levels, though real‑world use is often lower. Reports of dye sensitivity exist but consistent causal evidence at food‑use levels is limited. The dye is cosmetic only and does not improve the nutritional quality of food.
Key Research Points
High intake may exceed safety limit in some kids
EFSA kept the acceptable daily intake (ADI) at 5 mg/kg body weight/day and found that, if foods use the EU maximum permitted levels, some high‑consuming children could exceed the ADI; in practice many products use less color.
Impurity controls matter
Quality specifications tightly limit unsulfonated aromatic amines (e.g., aniline) to very low levels and require heavy‑metal limits; FDA also certifies each batch, so compliant manufacturing is key to minimize contaminants.
Rare sensitivity is reported
There are isolated reports of intolerance or hypersensitivity to indigotine, but robust causal evidence at food‑use levels is limited compared with some other dyes.
Overview
What is it?
Why is it used?
Origin
Indigo, a famous textile dye, has been used for centuries. In the late 1800s (Heumann process), chemists learned to make synthetic indigo from coal-tar aromatics. In the 1700s–1900s, sulfonating indigo with sulfuric acid produced a water-soluble blue derivative—indigo carmine—eventually adopted as FD&C Blue No. 2 in foods after the U.S. color-additive laws required testing and certification.
Process: Sulfonate indigo, then refine and certify
Steps
Chemicals
Research & Safety
Potential Concerns
Blue 2 is a highly refined synthetic dye made by sulfonating indigo and then purifying the resulting salt. The main issue for consumers is total exposure over time: EFSA modeling indicates that some children with very high intake of dyed foods could exceed the ADI if products use maximum permitted levels. Processing and refining matter because unsulfonated aromatic amines and heavy metals must be kept extremely low; certified, compliant batches meet these limits. Isolated sensitivity to dyes is reported, but strong evidence for consistent adverse effects from indigotine at typical food levels is limited. If you want to reduce exposure, choose dye‑free or naturally colored products and moderate intake of brightly colored sweets and drinks.
Potential Benefits
No demonstrated nutrimental benefit
Digestive Effects
At the very small amounts used in foods, most people do not notice digestive effects from Blue 2. Some individuals who report dye intolerance may experience nonspecific symptoms (for example, stomach upset or skin symptoms), but clear causal links for indigotine at food‑use levels are limited. At medical doses used for procedures (not dietary use), indigo carmine can discolor urine or stool; this is not expected from food amounts. If you suspect sensitivity, try a short dye‑free trial and reintroduce while reading labels to see if symptoms recur.
Limit Consumption
Children who frequently consume brightly colored products can have higher exposure; EFSA modeling suggests some high‑consuming children could exceed the ADI if foods are colored at maximum levels. For infants and toddlers, limiting low‑nutrient, vividly dyed foods is a simple way to keep exposure low. Individuals who believe they are sensitive to dyes may prefer dye‑free products since evidence for indigotine reactions is limited but not absent. Blue 2 is vegan/vegetarian and generally acceptable for Kosher and Halal diets, but it is typically not allowed in organic products.
Fact Sheet
Regulatory Status
ESG & Sustainability
Allergens and Diet
Natural Alternatives
Butterfly pea flower
Fruit/vegetable juice concentrates (blue hues)
Spirulina extract (phycocyanin)
Citations
FD&C Blue No. 2 — Listing of color additives subject to certification
2023-07-06U.S. FDA/eCFR • eCFR (21 CFR 74.102)
Regulatory Status of Color Additives: FD&C Blue No. 2
2022-03-04FDA CFSAN • FDA Color Additives Database
Follow-up of the re-evaluation of indigo carmine (E 132) as a food additive
2023-07-26EFSA Panel on Food Additives • EFSA Journal
Re-evaluation of Indigo Carmine (E132) as a food additive
2014-07-25EFSA ANS Panel • EFSA Journal
Indigotine — JECFA evaluation (ADI 0–5 mg/kg bw)
2018-01-01WHO/JECFA • WHO/JECFA Database
Indigotine — Specifications (impurity limits; assay ≥85%)
2010-01-01FAO/JECFA • FAO JECFA Monographs
Food colours list — Indigotine (E132) / FD&C Blue No. 2
2025-01-15Canadian Food Inspection Agency • CFIA
Indigo Carmine: Between Necessity and Concern
2023-08-01Ristea ME, et al. • PMC (Review)