Yellow Dye 5 vs Potassium Bromate: which is worse?

What is Yellow Dye 5?

Yellow Dye 5 (tartrazine) is a synthetic lemon-yellow azo dye derived from petroleum. It produces a bright, stable yellow color in acidic conditions and is one of the most widely used yellow dyes globally. Its chemical formula is C16H9N4Na3O9S2.

What is Potassium Bromate?

Potassium bromate (KBrO3) is an oxidizing agent used in commercial bread baking as a flour maturing agent and dough conditioner. It strengthens gluten networks, improves dough elasticity, and produces a more uniform, light-textured baked product. It is a white crystalline powder.

Documented risks

Yellow Dye 5: Yellow Dye 5 was one of six dyes studied in the landmark 2007 McCann et al. study in The Lancet. The study found statistically significant increases in hyperactivity in children ages 3 and 8–9 given a mixture containing tartrazine and sodium benzoate. EFSA reviewed the evidence and confirmed the effect was real, mandating the EU warning label from 2010. A 2012 review in Neurotherapeutics (Arnold et al.) confirmed that artificial food colors including tartrazine have a small but statistically significant adverse effect on children's behavior that is not confined to those with diagnosed ADHD. Tartrazine is one of the most documented causes of food dye hypersensitivity. Cross-reactivity with aspirin (acetylsalicylic acid, ASA) is well established in allergy literature: individuals with aspirin hypersensitivity have elevated risk of reacting to tartrazine. Symptoms include urticaria, angioedema, rhinitis, and in rare cases anaphylaxis. Prevalence of tartrazine sensitivity is estimated at 0.1% of the population but higher in aspirin-sensitive individuals. Because of this known hypersensitivity risk, the FDA specifically requires Yellow No. 5 to be declared by name on US food labels — an exceptional requirement not applied to most other additives, reflecting the FDA's acknowledgment of this real clinical concern. EFSA's 2009 re-evaluation found no evidence of genotoxicity in standard test systems at food use levels, setting an ADI of 7.5 mg/kg body weight, but noted in vitro evidence at higher doses. In April 2025, the FDA announced plans to phase out Yellow 5 along with other petroleum-based dyes.

Potassium Bromate: Potassium bromate is classified by the International Agency for Research on Cancer (IARC) as Group 2B — a possible human carcinogen — based on sufficient evidence in animals. This classification was formalized in 1999. The landmark toxicology study is Kurokawa et al. (1990), published in Environmental Health Perspectives (PMC1567851), which demonstrated that KBrO3 induces renal cell tumors (kidney cancer), mesotheliomas of the peritoneum, and follicular cell tumors of the thyroid in rats. Importantly, the researchers demonstrated KBrO3 is a complete carcinogen — it possesses both tumor-initiating and tumor-promoting activities for renal tumorigenesis. The mechanism of carcinogenicity involves generation of reactive oxygen species, particularly hydroxyl radicals and superoxide radicals. These radicals cause oxidative DNA damage, specifically 8-hydroxydeoxyguanosine (8-OHdG) formation in rat kidney cells — a well-characterized biomarker of oxidative DNA damage. California declared potassium bromate a known carcinogen under Proposition 65 in 1991, requiring cancer warning labels on California products containing it. Multiple advocacy organizations including CSPI (1999 petition) and EWG (2015 petition) have petitioned the FDA for a federal ban. As of 2025, the FDA has urged voluntary industry elimination since the early 1990s but has not issued a formal ban. Nephrotoxicity from high-dose potassium bromate is well documented in case reports of accidental or intentional poisonings: it causes irreversible renal tubular necrosis, permanent deafness (cochlear damage), and blindness (optic nerve damage). These effects occur at doses far above food consumption scenarios but demonstrate the compound's acute toxicological potency. FDA testing in 1999 found residual potassium bromate above expert-recommended safe limits in more than half of 17 tested bread and roll products, demonstrating that the 'it bakes off completely' argument does not always hold in commercial practice.