Red 3, formally known as erythrosine, is a synthetic dye made from a combination of carbon, hydrogen, iodine, sodium, and oxygen atoms. Its chemical formula is C₂₀H₆I₄Na₂O₅, which means every molecule of this cherry-red colorant contains four atoms of iodine. That iodine content is central to both how the dye works and why it has raised health concerns over the decades.
The Chemistry Behind the Color
Red 3 belongs to a class of compounds called xanthene dyes. Its molecular backbone is built from 20 carbon atoms arranged in interconnected rings, a structure common in many synthetic colorants. What makes Red 3 distinctive is those four iodine atoms attached to the ring structure. Iodine is a heavy element, and its presence is what shifts the compound’s light absorption into the range that produces a bright, cherry-red appearance in food and drinks. Two sodium atoms in the molecule make it water-soluble, which is why it dissolves easily into batters, frostings, and liquid medications.
The full molecule weighs about 880 grams per mole, relatively heavy for a food additive. For comparison, table sugar clocks in at 342 grams per mole. Most of that extra weight comes from the iodine, which accounts for roughly 58% of the molecule’s total mass.
Where Red 3 Has Been Used
Red 3 gives a vivid, slightly pinkish-red tone to a wide range of processed foods. The FDA lists its most common uses as candy, cakes and cupcakes, cookies, frozen desserts, and frostings and icings. It has also been used in certain ingested drugs, particularly pills and liquid medications where color helps patients identify their dose. The dye was already banned from cosmetics and externally applied drugs in 1990, but it remained legal in food and oral medications for decades afterward.
Why It Raised Safety Concerns
The iodine in Red 3 is also the reason it drew scrutiny from regulators. In animal studies, the dye interfered with thyroid hormone metabolism. The thyroid gland relies on iodine to produce hormones, and flooding the body with an iodine-containing compound appeared to disrupt that process. Rats fed diets containing 4% erythrosine over roughly two and a half years developed thyroid follicular cell adenomas (benign tumors) at a significantly higher rate than controls: 15 out of 69 male rats, compared to just 1 out of 69 in the control group.
The effect was dose-dependent and most pronounced in males. Female rats at the same dose did not show a statistically significant increase in tumors. And at lower doses (0.1% to 1% of the diet), neither sex developed tumors at rates that reached statistical significance. Malignant thyroid tumors (carcinomas) did not increase significantly in any group. Still, the benign tumor data in male rats at high doses was enough to trigger regulatory action.
The mechanism appears to work indirectly. Rather than damaging DNA the way many carcinogens do, Red 3 raises levels of thyroid-stimulating hormone (TSH) in the blood. In the studies, rats given even 0.25% erythrosine in their diet showed significantly elevated TSH levels within two weeks. Chronically elevated TSH pushes the thyroid to keep growing, and over time, that sustained growth signal can lead to tumors. This is sometimes called a “promotional” rather than a “genotoxic” mechanism, meaning the dye doesn’t mutate cells directly but creates conditions that encourage abnormal growth.
How Global Regulators Responded
International food safety bodies set strict limits on Red 3 intake long before the recent U.S. ban. The World Health Organization’s expert committee lowered its acceptable daily intake (ADI) to 0.6 mg per kilogram of body weight based on the thyroid hormone data. The European Scientific Committee for Food went further, setting its ADI at just 0.1 mg per kilogram of body weight.
In January 2025, the FDA announced it would revoke authorization for Red 3 in food and ingested drugs in the United States. Food manufacturers have until January 15, 2027, to reformulate their products, while drug manufacturers have until January 18, 2028. The decision was based on the Delaney Clause, a provision in U.S. law that prohibits any food additive shown to cause cancer in humans or animals, regardless of dose.
What Manufacturers Are Using Instead
With the phase-out underway, food companies are turning to natural pigments to replace Red 3’s characteristic hue. One of the most promising alternatives comes from anthocyanins, the pigments that give blackberries, red cabbage, and grapes their deep colors. Researchers at Ohio State University have developed modified versions of these pigments called pyranoanthocyanins, which hold their color more reliably under heat, light, and varying acidity levels. These compounds can produce stable shades of red, orange, and yellow without synthetic chemistry. Other common replacements include beet juice concentrate and pigments derived from red radishes or sweet potatoes, though each comes with its own limitations in terms of flavor, stability, and cost.