Blue Dye 2 vs Butylated Hydroxytoluene: which is worse?

What is Blue Dye 2?

Blue Dye 2 (Indigotine/Indigo Carmine) is a synthetic disulfonated derivative of indigo. Unlike natural indigo from the indigo plant, the FD&C version is synthetically manufactured from petroleum. It produces a dark royal blue to indigo color and is used in food, pharmaceuticals, and medical diagnostics.

What is Butylated Hydroxytoluene?

Butylated hydroxytoluene (BHT) is a synthetic phenolic antioxidant preservative derived from petroleum. A white crystalline solid with formula C15H24O, it prevents fat oxidation in processed foods, cosmetics, and industrial applications. Often used synergistically with BHA.

Documented risks

Blue Dye 2: Animal studies conducted in the 1980s found that high-dose Blue Dye 2 caused brain tumors in male rats. An NTP bioassay (1987) found statistically significant increases in brain gliomas (astrocytomas) in male rats given high doses. The FDA reviewed these findings and determined that the doses far exceeded typical human dietary exposure. Nonetheless, the tumor finding remains in the scientific record as a concerning data point. EFSA's 2010 safety evaluation of Indigo Carmine (E132) reached an unusual conclusion: it could not establish an ADI due to data limitations, including the brain tumor findings. This means EFSA adopted an implicit conservative position — it neither declared Blue 2 safe nor formally banned it, but the absence of an established ADI signals scientific uncertainty. In medical diagnostic use, high intravenous doses of Indigo Carmine can cause hypertension, bradycardia, and in rare cases anaphylaxis. These are dose-specific clinical pharmacological effects, not relevant to dietary consumption at food use levels. Blue 2 was not included in the 2007 Lancet hyperactivity study. Limited direct research links Blue 2 to behavioral effects. The FDA's April 2025 announcement includes Blue 2 in the class of petroleum-based synthetic dyes to be phased out of the US food supply, reflecting updated policy on the category rather than specific new Blue 2 toxicity data.

Butylated Hydroxytoluene: BHT has complex, bidirectional carcinogenicity data — some NTP bioassays found liver tumors in female mice at high doses, while other studies suggested BHT might inhibit cancer initiation. IARC has not formally classified BHT due to conflicting evidence. A 2017 study linked BHT to thyroid hormone disruption in female rats. The American Academy of Pediatrics (2018) recommended reducing synthetic preservative exposure including BHT in children. Kellogg's uses vitamin E in European versions of cereals that contain BHT in US versions — a commercially meaningful substitution.