Ethoxyquin is a synthetic antioxidant used primarily to prevent fats from going rancid in animal feed, pet food, and certain agricultural products. Originally developed as a rubber stabilizer, it was later adopted by the food and agriculture industries because it is cheap to produce, highly effective at slowing fat breakdown, and helps preserve vitamins A and E. It has a complicated regulatory history: still permitted in the United States at limited concentrations, but suspended entirely in the European Union since 2017.
How Ethoxyquin Works
Fats in animal feed and pet food break down when exposed to oxygen, a process called lipid oxidation. This makes the food smell bad, destroys nutritional value, and can produce harmful byproducts. Ethoxyquin interrupts this chain reaction by reacting with the unstable oxygen molecules (free radicals) that drive fat breakdown. When it neutralizes a free radical, ethoxyquin transforms into a dimer compound that itself has moderate antioxidant activity, essentially extending the protective effect over time.
Beyond preventing rancidity, ethoxyquin stabilizes fat-soluble vitamins, particularly A and E, which degrade quickly in stored feed. This dual function made it attractive to feed manufacturers starting in the mid-20th century, when the Monsanto Company refined it for commercial use in animal nutrition.
Where Ethoxyquin Shows Up
Most people encounter ethoxyquin indirectly. Its main uses include:
- Pet food and animal feed: Canned pet food, poultry feed, and farmed fish feed are the most common applications. It appears on ingredient labels as “Ethoxyquin, a preservative” or with the statement that it was “added to retard the oxidative destruction of carotene, xanthophylls, and vitamins A and E.”
- Fish meal: Fish meal is particularly prone to spontaneous heating and even combustion during shipping because of its high fat content. Ethoxyquin is added to stabilize it for safe transport.
- Spices: Paprika and chili powder sometimes contain ethoxyquin to preserve their red color, which fades as pigments oxidize. Commercial paprika samples have been found with levels up to 63 ppm, and chili powder up to 20 ppm.
- Fruit storage: Ethoxyquin prevents “superficial scald,” a brown discoloration that develops on pears and apples during cold storage. D’Anjou pears treated with 1,000 ppm of ethoxyquin stayed scald-free for four months, while untreated fruit developed the disorder after just three months.
Regulatory Limits in the U.S.
The FDA permits ethoxyquin in complete animal feed and forage at a maximum of 150 ppm (0.015%). For dog food specifically, the FDA requested that manufacturers voluntarily lower their use to 75 ppm, half the legal ceiling. Industry testing explored whether even lower concentrations, between 30 and 60 ppm, could still protect dog food from oxidation.
Any product containing ethoxyquin must declare it on the label. There is no allowance for unlisted use, so checking ingredient labels on pet food is a reliable way to know whether it is present.
Why the EU Suspended It
In June 2017, the European Commission suspended ethoxyquin as a feed additive for all animal species. The decision followed a safety review by the European Food Safety Authority, which found it could not confirm the additive was safe for consumers, certain animal groups, or the environment.
The core problem was a manufacturing impurity called p-phenetidine, a recognized possible mutagen that remains in the finished product. Because there was not enough data on whether p-phenetidine accumulates in meat, milk, or eggs from animals fed ethoxyquin-treated diets, EFSA could not rule out a risk to people eating those products. The agency also flagged concerns about contamination of aquatic ecosystems, particularly around sea-cage fish farms, and a risk to organisms living in marine sediment. Workers handling the additive were identified as a concern too, since inhalation exposure to the p-phenetidine impurity needed to be minimized.
EFSA did note that ethoxyquin itself does not appear to be genotoxic or carcinogenic, and that meat-producing animals like chickens, pigs, cattle, rabbits, and fish tolerate it at authorized levels. The suspension was driven by data gaps and the impurity profile rather than by direct proof of harm from ethoxyquin alone.
What Animal Studies Show
The toxicity picture for ethoxyquin comes mostly from decades-old feeding studies in dogs, rats, and mice. The liver and kidneys are the organs most consistently affected.
In dogs fed ethoxyquin at doses of 10 mg per kilogram of body weight and above, liver function tests showed signs of dysfunction. At 50 mg/kg, blood tests revealed reduced red blood cell counts and abnormally dark urine. The highest dose group, 100 mg/kg, developed effects severe enough that researchers stopped feeding them after just six weeks. Across all dose levels, heart, liver, and kidney weights increased relative to body size, and microscopic examination showed liver stress and fatty degeneration in the kidneys.
Rats told a similar story. Short-term studies found kidney lesions in males at 500 ppm and liver changes at 2,000 ppm. Over longer periods of 200 to 400 days, males developed kidney inflammation, liver changes, and thyroid tissue overgrowth. In reproduction studies, litter sizes dropped at 375 ppm and above, and at 1,125 ppm there were more stillbirths and fewer pups surviving to weaning. Tumors did occasionally appear after 700 days, but at rates no different from untreated control animals, suggesting ethoxyquin itself is not a direct cancer cause.
One of ethoxyquin’s breakdown products, called ethoxyquin quinone imine, raises more concern. It has structural features associated with mutagenicity and DNA damage, and in animal testing it caused toxic effects on red blood cell production. Another breakdown product, the dimer, caused fatty liver changes and cell death in mouse livers at doses above 10 mg/kg per day. In salmon, high ethoxyquin exposure altered liver and kidney tissue under the microscope.
Skin Reactions in Workers
People who handle ethoxyquin directly face a different risk. Multiple cases of dermatitis have been documented among workers handling freshly sprayed apples still wet with ethoxyquin solutions. Patch testing confirmed these reactions were not simple irritation but true allergic sensitization, meaning the immune system had developed a lasting reaction to the chemical. This is primarily a concern for agricultural and manufacturing workers, not consumers exposed to trace residues in food.
How to Identify It on Labels
On pet food and animal feed labels in the U.S., ethoxyquin must be listed by name. You will not find it hidden under vague terms like “antioxidants” or “preservatives” alone. Its chemical name is 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, though this rarely appears on commercial packaging. If you are looking to avoid it, scan for the word “ethoxyquin” in the ingredient list or the preservative statement. Many premium pet food brands now market themselves as ethoxyquin-free, using alternatives like tocopherols (vitamin E compounds) or rosemary extract instead.
One less obvious route of exposure: fish meal used as an ingredient in pet food may have been treated with ethoxyquin before the pet food manufacturer ever received it. In that case, the ethoxyquin was not added by the pet food company, but it can still be present in the final product. Some brands specify that their fish meal sources are ethoxyquin-free for this reason.