What is E324?

Complete guide to understanding ethoxyquin in your food

The Quick Answer

E324 is ethoxyquin, a synthetic antioxidant used primarily in animal feed to prevent fats from becoming rancid, and in limited spices to preserve color.

It’s a quinoline-based synthetic chemical compound that has been used for decades to preserve polyunsaturated fats in animal feed, particularly fishmeal. Originally also used as a pesticide to prevent browning of pears.

Critical regulatory status: E324 is PROHIBITED in the European Union (suspended June 2017) but still approved in the United States. This significant regulatory divergence reflects ongoing safety concerns identified by European regulatory authorities.

What Exactly Is E324?

E324 is ethoxyquin, a synthetic quinoline-based antioxidant compound designed to prevent oxidation (rancidity) of fats and oils in animal feed.

More specifically, it’s a synthetic aromatic organic compound (C14H19NO) that works at the molecular level to prevent the oxidation of polyunsaturated fatty acids. Unlike natural antioxidants like vitamin C or vitamin E, ethoxyquin is entirely laboratory-synthesized.

E324 was historically regarded as the “most effective antioxidant” for preventing polyunsaturated fat oxidation in fishmeal, making it valuable for preventing spontaneous combustion during shipping and storage—a critical safety concern for the shipping industry.

It remains stable at the high temperatures required for food processing, making it practical for extrusion of pet foods and other processed animal feeds.

Regulatory Status: The E324 Divergence

This regulatory split reflects a critical difference in how the EU and USA assessed E324’s safety profile. The EU’s suspension was based on insufficient data to demonstrate safety, while the FDA determined it could be safely used when properly regulated.

Why Was E324 Suspended in the EU?

The European Food Safety Authority (EFSA) suspended E324 due to critical data gaps and specific safety concerns.

In November 2015, the EFSA published a report identifying two key gaps that prevented conducting a full safety risk evaluation:

1. Insufficient data on adverse effects on animal health, human health, and the environment
2. Specific safety concerns about two compounds: a metabolite called “ethoxyquin quinone imine” (possibly genotoxic) and an impurity called “p-phenetidine” (possibly mutagenic from manufacturing)
3. Lack of adequate studies to assess consumer exposure and dietary intake

Because the reauthorization procedure for feed additives requires robust safety data, and the applicant could not provide sufficient evidence, the European Commission formally suspended authorization on June 28, 2017.

Where You’d Find E324 (Historical and Current)

E324 locations differ dramatically by region due to regulatory divergence:

European Union: NOWHERE—it is prohibited
United States: Animal feed (pet food, livestock feed, fishmeal); chili powder, paprika, ground chili
Norway & France: Farmed salmon feed
Australia: Not permitted

Hidden presence in USA: Often not listed on labels because E324 frequently enters products indirectly through feed ingredients (fishmeal, poultry meal) rather than being added directly. This means it can be present in virtually any pet food without appearing on the ingredient list.

How E324 Works in Food

E324 serves primarily as a fat oxidation preventative in animal feed.

Fat oxidation prevention: E324 prevents polyunsaturated fats from becoming rancid by inhibiting oxidation at the molecular level. This preserves nutritional quality, maintains available calories, and prevents flavor degradation.

Temperature stability: Unlike some antioxidants that degrade during processing, E324 remains stable at the high temperatures (extrusion) required for pet food manufacturing.

Nutrient preservation: E324 preserves vitamin E and carotenoids in dried forage crops (corn, wheat, oats) and animal feeds.

Fire prevention: E324 prevents spontaneous combustion of fishmeal during storage and sea transport—a critical safety function. The International Maritime Organisation legally requires an antioxidant like E324 for fishmeal shipping.

Color preservation: In spices, E324 prevents color loss due to oxidation of natural carotenoid pigments (e.g., the red color in paprika and chili).

Is It Safe?

Safety assessment of E324 is complex due to the EU-USA regulatory divergence reflecting fundamentally different conclusions about safety evidence.

FDA Position (USA)

The FDA has ruled that ethoxyquin “may be safely used in animal feeds” when used according to regulations. The FDA acknowledged that studies show elevated liver enzymes and accumulation of certain compounds in the liver in some animals, but concluded these do not have known health consequences at approved use levels.

In 1997, the Center for Veterinary Medicine asked manufacturers to voluntarily limit ethoxyquin to 75 ppm (75 mg/kg) as a precautionary measure until further evidence, though most pet foods have never exceeded this limit.

EFSA Position (EU – 2015)

The EFSA reached a different conclusion: they determined that insufficient data exists to safely approve E324. Specifically, they identified:

– Insufficient data on safety for target animals, consumers, and the environment
– Metabolite concern: Ethoxyquin quinone imine (a breakdown product) possibly genotoxic
– Impurity concern: p-phenetidine (manufacturing impurity) possibly mutagenic
– Inconclusive assessment: Could not determine safety with available evidence

This assessment led to the 2017 suspension, reflecting the principle that substances should not be used without adequate safety evidence.

Known Biochemical Effects

Animal studies have identified specific biochemical changes from E324 exposure:

– Accumulation of protoporphyrin IX in liver
– Elevated liver enzymes in blood
– Loss of weight (in some cases)
– Changes in liver, kidney, urinary bladder, and mitochondria
– Anemia and lethargy
– Discolored urine, skin, or fur
– Increased mortality (at high doses)
– Immune system effects
– Potential to induce allergies (contact exposure)

Important note: These biochemical changes do not necessarily translate to visible health problems, and the FDA maintains no health consequences are known from these findings at approved use levels.

Indirect Food Exposure (USA)

A critical concern for USA consumers: E324 often appears in food without being listed on the label.

E324 frequently enters animal feed products indirectly through feed ingredients (fishmeal, poultry meal, fish oil) that already contain it, rather than being added directly to the finished food. This means:

– It can be present in pet food even if not listed on the label
– It’s almost impossible for consumers to avoid it completely
– Residues of E324 pass through to food of animal origin (meat, eggs)
– USA tolerance: 5 mg/kg in uncooked meat fat; 3 mg/kg in poultry fat and liver

How E324 Is Made

E324 is a wholly synthetic compound created through chemical synthesis.

Ethoxyquin is manufactured through organic chemistry laboratory processes—not extracted from nature or produced through fermentation. The manufacturing process can produce impurities, particularly p-phenetidine, which the EFSA identified as a concern. Feed manufacturers have taken steps to significantly reduce p-phenetidine levels in products.

Original Use: Pear Browning Prevention

E324 was originally registered as a pesticide in 1965 to prevent post-harvest scald (browning) in pears.

Under the commercial name “Stop-Scald,” it was applied as a drench or impregnated wrap to freshly harvested pears to prevent browning during storage. This pear application remains approved in both the USA and EU, even after the feed additive suspension in the EU. This agricultural use is separate from food additive use.

Vegan and Dietary Status

E324 is technically vegan (not animal-derived), but its approval status makes this largely irrelevant:

– Synthetic: Wholly laboratory-synthesized; not natural
– Technically vegan ✓ – Not animal-derived
– Technically vegetarian ✓ – Not animal-derived
– Natural: No—entirely artificial
– Gluten-free: Yes

Comparison with Other Antioxidants

E324 differs from other synthetic and natural antioxidants:

– BHA (E320) & BHT (E321): Similar synthetic antioxidants; different chemical structure
– TBHQ (E319): Another synthetic antioxidant
– Vitamin C (E300): Natural antioxidant; different mechanism
– Vitamin E (E306-309): Natural antioxidant; different mechanism
– Propyl gallate: Phenol derivative synthetic antioxidant

E324 was historically considered most effective for preserving polyunsaturated fats in fishmeal—a distinction that contributed to its 35+ year use history.

Public Concern vs. Regulatory Assessment

E324 generates significant public concern, but experts point to potential confusion about sources of concern.

Much of the fear about ethoxyquin in pet foods stems from its use as a pesticide and in rubber manufacturing—applications that have nothing to do with food safety. Food safety experts generally agree that when used at approved levels in animal feed, ethoxyquin is not toxic.

The EU suspension, however, reflects not that E324 is proven dangerous, but rather that safety evidence is insufficient to continue approval under regulatory standards requiring robust proof of safety.

The Bottom Line

E324 (ethoxyquin) is a synthetic antioxidant used primarily in animal feed to prevent fat oxidation, with sharply divergent regulatory status across regions.

It’s a wholly synthetic quinoline-based compound created through laboratory chemical synthesis.

European Union: Completely PROHIBITED since June 28, 2017. Do NOT find E324 in any EU food or feed products.

United States: Still APPROVED for animal feed and limited spices (chili powder, paprika, ground chili). Present in USA pet foods and may not appear on labels if from feed ingredients.

Safety assessment: The FDA considers it safe at approved levels. The EFSA determined insufficient data exists for safety approval. This represents a genuine difference in regulatory philosophy and evidence standards.

Known effects: Liver enzyme elevation and protoporphyrin accumulation documented in animals at various doses. Long-term health consequences unclear.

The regulatory split reflects how seriously the EU and USA differ on food additive risk assessment, with the EU taking a more precautionary stance requiring stronger evidence before approval.

If you’re in the EU, E324 is not a concern—it’s completely prohibited. If you’re in the USA, it may be present in pet food and spices without appearing on labels.