What ethoxyquin is
Ethoxyquin (6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline) is a synthetic phenolic antioxidant developed by Monsanto in the 1950s. It is used in pet food, fish meal, paprika, chili powder, and as an apple-blemish-prevention treatment. The molecule is highly effective at preventing lipid peroxidation, particularly in long-chain polyunsaturated fatty acids (the fats most prone to going rancid), which is why it has been the dominant preservative in fish meal for half a century.
Per US 21 CFR 573.380, ethoxyquin is permitted as a feed additive in animal feeds at concentrations not to exceed 150 ppm (parts per million). In 1997, the FDA Center for Veterinary Medicine asked the pet food industry to voluntarily reduce its use to 75 ppm based on emerging concerns about chronic-exposure data. Several large manufacturers complied; some did not.
The EU ban (June 2017)
On June 28, 2017, the European Commission suspended the authorisation of ethoxyquin as a feed additive for all animal species. The suspension was triggered by the EFSA 2015 safety opinion, which concluded the agency could not rule on safety because of significant data gaps in the dossier submitted by the joint manufacturer FEFANA asbl. Specific concerns included: (1) the toxicology of the metabolite ethoxyquin quinone imine, which showed potential genotoxicity in vitro; (2) the presence of p-phenetidine, a manufacturing impurity, which is a possible mutagen; and (3) gaps in environmental fate data.
EFSA reopened the assessment in 2022 (EFSA Journal 7166, March 3, 2022). The new opinion acknowledged that many of the original data gaps had been clarified by additional studies submitted since 2017. However, the p-phenetidine impurity concern remained unresolved — the regulatory bar for genotoxic impurities is essentially absolute, and the EU did not lift the ban. As of 2024, ethoxyquin remains banned in EU animal feed.
The fish meal loophole
This is the most important fact about ethoxyquin in US pet food: it can be present in your dog's food and not be declared on the label. The mechanism: US Coast Guard hazardous-materials regulations have historically required oxidation suppression in fish meal during ocean transport, because high-fat fish meal is one of the few cargoes that can spontaneously combust when oxidizing. Ethoxyquin has been the most-used preservative for this purpose. When a kibble manufacturer purchases preserved fish meal, the ethoxyquin travels with the ingredient. Per FDA labeling rules, the manufacturer must declare any preservative they themselves add — but they are not required to declare a preservative their supplier added if it falls below the threshold of being a meaningful component of the finished product.
The result: a bag of fish-formula dog food labeled “preserved with mixed tocopherols” can contain undeclared ethoxyquin in the fish meal. This is legal under FDA rules. It is increasingly rare among premium fresh-fish brands (Acana, Orijen, ZIWI, and several others source their fish from suppliers that use non-ethoxyquin preservation), but remains common in mid- and lower-tier fish-formula kibble.
How to detect ethoxyquin without testing the food
Three label-reading heuristics work in lieu of laboratory testing:
- Read the ingredient list for explicit mention. If “ethoxyquin” appears anywhere — including in a parenthetical like “fish meal (ethoxyquin-free)” or “fish meal (preserved with mixed tocopherols)” — the manufacturer is signaling. The negative-stated assurance is itself meaningful.
- Check for “ethoxyquin-free” supplier certification language on the brand's website or FAQ. Brands that source non-ethoxyquin fish meal typically advertise it; brands that don't, don't.
- Default-assume any unmodified “fish meal” in a low- or mid-tier kibble carries ethoxyquin. The supplier base for low-cost fish meal still relies on ethoxyquin.
What KibbleIQ does with this
The KibbleIQ Dry Kibble Rubric v15 deducts when ethoxyquin is declared on the ingredient list. We do not double-deduct if BHA or BHT is also declared — the deduction is for the synthetic-preservation strategy, not the molecule. Because of the fish-meal loophole, we cannot reliably score for undeclared ethoxyquin from supplier-side preservation, and our rubric does not penalize it on suspicion. Brands that affirmatively declare “ethoxyquin-free fish meal” or document their supplier preservation chain earn no positive credit beyond the deduction's absence — transparency is the baseline expectation.
To check whether your current kibble declares ethoxyquin, paste the ingredient list into the KibbleIQ analyzer. For the broader synthetic-preservation question, see our explainer on BHA and BHT and our review-driven guide to the best dog food for skin and coat (where omega-3 from fish-derived sources matters most).