We'd avoid · Synthetic antioxidant

Ethoxyquin

Also appears on labels as: ethoxyquin (a preservative), often inside "fish meal"

A synthetic antioxidant originally developed as a rubber stabilizer, now used mainly to keep fish meal from oxidizing in transit.

Watched ingredients get highlighted on every product panel you open.

Where it comes from: Chemical synthesis. Often added at the fish meal supplier, before the ingredient ever reaches the pet food plant.
Why it's in the product: Prevents fish meal from combusting or spoiling during shipping and storage.
Safety and toxicity: After long-term dog feeding studies raised liver questions, the FDA asked manufacturers to voluntarily halve the maximum level. The EU suspended its use in animal feed in 2017 pending safety data. It remains legal in the US at limited levels.
Interactions and who should be careful: The disclosure problem is the real story. Ethoxyquin added upstream by a fish meal supplier does not always have to appear on the finished label, so its absence from a panel is not proof of absence from the bag. Panels that do name it are being more honest than the ones that stay quiet.

What the research says

Ethoxyquin keeps fish meal from oxidizing in transit, and US rules allow it in pet food at limited levels. After long-term feeding studies raised questions about liver effects in dogs, the FDA asked manufacturers to voluntarily halve the maximum level, and the EU suspended its use in animal feed in 2017 pending safety data.

The tricky part is disclosure: ethoxyquin can arrive inside an ingredient like "ocean fish meal" and appear only in parentheses, or in some cases not at all if it was added before the ingredient reached the manufacturer. Panels that name it, to their credit, are at least telling you. Fish-first foods preserved with mixed tocopherols avoid the question entirely.

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General reference, not veterinary advice. Dose, breed, and existing conditions change the answer, so talk to your vet before changing what your pet eats. Think we got this wrong? Tell us and we log it publicly.