Ethoxyquin in dog and cat food

Is it OK for dogs and cats?

Dogs

US rules allow ethoxyquin in dog food up to 150 ppm, and the label must name it even when it comes in through an ingredient such as fish meal. In 2015 EFSA put the highest potentially safe level for dogs at 11 mg per kg of complete feed. In 2022 it could not conclude on any safe level for long-living animals because of an impurity, and the EU denied authorisation that year.

Cats

Less is known for cats. EFSA could not set any safe level for cats, citing their limited ability to conjugate (process) aromatic substances and the lack of tolerance studies. US rules and labelling are the same as for dogs.

How settled this is: Limited by regulators

What ethoxyquin is

Ethoxyquin (6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline) is a synthetic antioxidant. It was first developed in the rubber industry to stop rubber cracking from oxidation, and was later adapted as a feed preservative. It is made from p-phenetidine, which can remain in the additive as an impurity. In the EU's feed-additive system it had the number E 324.

Why it is in pet food

It slows the oxidation of fats and fat-soluble nutrients. The US feed rule for ethoxyquin (21 CFR 573.380) allows two uses. One is as a preservative that slows oxidation of carotene, xanthophylls and vitamins A and E in animal feed and fish food. The other is as an aid that helps prevent organic peroxides forming in canned pet food. International maritime rules require fish meal to be stabilised against spontaneous combustion when it is made. The options are 400–1,000 mg/kg of ethoxyquin or liquid BHT, or 1,000–4,000 mg/kg of powdered BHT. So ethoxyquin can reach pet food through fish meal, and a 2013 review also lists fish oils among products where it can be found. EFSA found it an effective feed antioxidant at 25–50 mg/kg of complete feed.

What it does in the food

It has no nutritional role. It is a technological additive (an antioxidant) that protects vitamins A and E, carotenoids and fats from breaking down during storage.

Safety and limits

United States: FDA approves ethoxyquin as a food additive for animal feed, at no more than 150 ppm in the finished feed. The label must say 'Ethoxyquin, a preservative' or 'Ethoxyquin added to retard the oxidative destruction of carotene, xanthophylls, and vitamins A and E'. This applies whether ethoxyquin is added directly or comes in through an ingredient. A 2013 review reports that FDA once asked makers to voluntarily lower the level in complete dog foods from 150 ppm to 75 ppm. European Union: the EU suspended ethoxyquin's authorisation in 2017 and denied it in August 2022. The Commission found it had not been established that ethoxyquin has no adverse effect on animal health, human health or the environment. For animals, the unresolved concern was p-phenetidine, an impurity that is a recognised possible mutagen (a substance that may cause genetic mutations). In 2015 EFSA could not rule out genotoxicity of a breakdown product, ethoxyquin quinone imine. After new studies, its 2022 opinion concluded that this breakdown product does not pose a genotoxicity concern. In 2022 EFSA considered 50 mg/kg of complete feed safe for the farm species tested and extended this to all species except cats. Because of p-phenetidine, though, it could not conclude on safety at any level for long-living and reproductive animals. Dogs: a 2013 review describes dogs as the animals most susceptible to ethoxyquin's harmful effects. EFSA's lowest no-observed-adverse-effect level, 2 mg per kg of body weight per day, comes from a 90-day study in Beagle dogs and is based on liver cell damage (hepatocellular necrosis). EFSA's 2015 opinion put the highest potentially safe level for dogs at 11 mg/kg of complete feed. The 2013 review cites 100 ppm in feed (about 2.5 mg/kg body weight a day) as a minimal-effect level for clinical signs and liver effects in dogs. From 1988, FDA received reports from dog owners and vets of liver, kidney, thyroid, reproductive and skin problems. These were reported observations, not controlled findings. Cats: EFSA could not set a safe level, citing cats' limited capacity to conjugate aromatic substances and the absence of tolerance studies.

What depends on the amount and the recipe

The amount in the finished food. The US maximum is 150 ppm, and a 2013 review reports an earlier FDA request for 75 ppm in complete dog foods. Whether it came in through fish meal or another ingredient, which the label must still declare. The species, since there are no safety data for cats. Where the food is sold: ethoxyquin is permitted in US animal feed, but its EU authorisation as a feed additive was suspended in 2017 and denied in 2022.

Not the same as

• BHT (E321) — A different synthetic antioxidant. International rules allow it as an alternative to ethoxyquin for stabilising fish meal.
• BHA (E320) — A different synthetic antioxidant. The 2022 EFSA opinion notes ethoxyquin may be combined with BHA and/or BHT in feed.

Sources

1. Labeling and Use of Ethoxyquin in Animal Feed — U.S. Food and Drug Administration, Center for Veterinary Medicine, 2024. Ethoxyquin is an approved food additive for animal feed; required label statements when added directly or through an ingredient; 150 ppm maximum in complete animal food.
2. 21 CFR 573.380 Ethoxyquin in animal feeds (4-1-25 edition) — U.S. Government Publishing Office (Code of Federal Regulations), 2025. Permitted uses (preservative for carotene, xanthophylls, vitamins A and E in animal feed and fish food; preventing organic peroxides in canned pet food); 150 ppm maximum; label requirements.
3. Commission Implementing Regulation (EU) 2022/1375 concerning the denial of authorisation of ethoxyquin as a feed additive — Publications Office of the European Union, 2022. EU denial adopted 5 August 2022; 2017 suspension; 2015 EFSA concerns about p-phenetidine and ethoxyquin quinone imine; 2022 EFSA could not conclude on safety for long-living and reproductive animals because of p-phenetidine; not established that there is no adverse effect; E 324 designation.
4. EFSA FEEDAP Panel (2022). Safety and efficacy of a feed additive consisting of ethoxyquin for all animal species. EFSA Journal 20(3):7166 — EFSA Journal (via PubMed Central), 2022. Made from p-phenetidine, a possible mutagen; 50 mg/kg safe for tested farm species and extrapolated to all species except cats, but no conclusion at any level for long-living and reproductive animals; ethoxyquin quinone imine concluded not a genotoxicity concern; cats' limited capacity to conjugate aromatic substances; NOAEL 2 mg/kg bw/day from a 90-day Beagle study based on hepatocellular necrosis; 11 mg/kg potentially safe for dogs (2015 opinion); IMO fish-meal stabilisation rule; possible combination with BHA/BHT; efficacy at 25–50 mg/kg.
5. Błaszczyk A, Augustyniak A, Skolimowski J (2013). Ethoxyquin: an antioxidant used in animal feed. Int J Food Sci 2013:585931 — International Journal of Food Science (via PubMed Central), 2013. Origin in the rubber industry and later use as a feed preservative; FDA request for optional lowering in complete dog foods from 150 to 75 ppm; reports from dog owners and vets to FDA from 1988; dogs the most susceptible animals; 100 ppm minimal-effect level for clinical signs and liver effects in dogs; presence in fish meal and fish oils.

Checked against these sources on 2026-10-15. Definitions are in our own words. This is a reading aid, not veterinary advice: a vet who knows your animal comes first.