Short answer: BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene) are synthetic antioxidant preservatives classified IARC Group 2B (possibly carcinogenic to humans). The US FDA permits them at GRAS status; the National Toxicology Program lists BHA as reasonably anticipated to be a human carcinogen. KibbleIQ deducts points when either appears in the ingredient list because alternatives exist and lifetime daily exposure in pet food is not the human exposure model the original safety thresholds were derived from.

What BHA and BHT are

BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene) are phenolic synthetic antioxidants developed in the 1940s to prevent rancidity in fats and oils. They donate a hydrogen atom to the peroxyl radicals formed during lipid autoxidation, terminating the chain reaction that turns rendered animal fat from edible into rancid. In dog food, they appear most often in low- to mid-tier kibble where the fat coat applied after extrusion needs to survive 18-24 months of warehouse storage and retail shelf time.

Per the US FDA, both compounds are listed as Generally Recognized As Safe (GRAS) for use in animal feed at 21 CFR 582.3169 (BHA) and 21 CFR 582.3173 (BHT). The European Food Safety Authority (EFSA) reassessed BHA in 2011 and BHT in 2012 and concluded both fall within an Acceptable Daily Intake (ADI) for typical human exposure, but maintained the preservatives as feed additives subject to a 150 mg/kg cap per FEDIAF. AAFCO Official Publication caps total antioxidants in animal feed at 200 ppm of fat content combined.

The cancer-classification evidence

The IARC (International Agency for Research on Cancer) classifies BHA as Group 2B — possibly carcinogenic to humans — based on the Ito 1986 forestomach-tumor study in rats and Williams 1990 follow-up reviews. The US National Toxicology Program's 15th Report on Carcinogens (NTP 2021) lists BHA as “reasonably anticipated to be a human carcinogen,” one tier above IARC's classification. BHT was assessed by the National Toxicology Program in 1979 and 1983; the data were inconclusive for carcinogenicity but showed liver enzyme induction, thyroid hyperplasia, and hemorrhagic effects at high doses.

The forestomach tumors observed in rodent studies are a contested data point. Humans do not have a forestomach; the tissue is an evolutionary holdover present in rodents and ruminants but absent in primates and dogs. EFSA's 2011 reassessment leaned on this anatomical mismatch to conclude human exposure at typical food levels is not concerning. The pet-food question is whether the lifetime daily exposure model in a 14-year-old dog eating the same kibble formula starting in puppyhood matches the species and exposure assumptions the original safety thresholds were derived from. That model has not been published.

How they appear on dog food labels

Per AAFCO labeling rules, when BHA or BHT preserves the fat in pet food, the label must declare it. The standard phrasing is “preserved with BHA” or “BHT (a preservative)” appearing alongside the fat source, e.g., “chicken fat (preserved with BHA and citric acid).” A loophole: when BHA or BHT is added at the rendering stage to a meat meal supplier (not by the kibble manufacturer), the synthetic preservative may not appear on the bag at all because it travels with the supplier ingredient and falls below FDA's incoming-ingredient declaration threshold. This is one reason chicken meal and fish meal in low-tier kibble can carry undeclared synthetic preservatives.

The natural alternatives

Three preservation systems dominate the higher-tier dog food market and avoid the synthetic phenolics entirely:

  • Mixed natural tocopherols — the four naturally occurring vitamin E isomers (alpha, beta, gamma, delta) extracted from soybean or sunflower oil. Effective antioxidant; shelf life typically 9-12 months.
  • Rosemary extract — standardized for carnosic acid and carnosol content. Pairs well with mixed tocopherols and gives the food a distinct herbaceous aroma. Per the Yang 2018 review (Food Chemistry), comparable peroxide-value control to BHT in poultry-fat models.
  • Ascorbic acid (vitamin C) — water-soluble; usually combined with tocopherols since it works on the oil-water interface rather than within the fat itself.

The trade-off is shelf life. A bag preserved with mixed tocopherols typically holds quality for 9-12 months from manufacture; a bag preserved with BHA-BHT-ethoxyquin can hold 18-24 months. Higher-tier brands compensate with bag-specific best-by date stamping, smaller bag sizes, and cold-chain warehouse logistics.

What KibbleIQ does with this

Under the KibbleIQ Dry Kibble Rubric v15, BHA and BHT each trigger a small but cumulative deduction when declared on the ingredient list. The rationale is precautionary: the safety classifications are not benign (Group 2B + NTP 15th Report listing for BHA), the pet-food lifetime-exposure model has not been validated, and natural alternatives exist at modest cost. We do not deduct for ethoxyquin separately if BHA or BHT is already present (the deduction is for the preservation strategy, not the molecule); we cover ethoxyquin in its own dedicated explainer. Brands that proactively switch to mixed tocopherols or rosemary extract earn no positive credit beyond the absence of the deduction — the absence of synthetic preservatives is the baseline expectation.

Want to know if your current bag is preserved synthetically? Paste the ingredient list into the KibbleIQ analyzer, or browse our worst dog foods to avoid guide. For more on the preservation trade-off, see our explainer on chicken by-product meal (where supplier-side BHA-BHT often hides) and our overall best dog food picks (all of which use natural preservation systems).