Shun NagaiTo maintain freshness and preserve nutritional value in pet food, preventing the oxidation of fats and vitamins is essential. For this purpose, antioxidants (also called oxidative inhibitors) are widely used. By slowing or stopping oxidative chain reactions, antioxidants help prevent quality deterioration, rancidity, and off-flavors.
In pet food, antioxidants are broadly categorized into synthetic antioxidants and natural antioxidants. Both types work primarily on lipids by donating hydrogen to peroxide radicals, thereby interrupting oxidation and stopping the reaction from progressing.
This article summarizes the main antioxidant types used in pet food, their characteristics, applicable safety standards, and common consumer misunderstandings.
Synthetic Antioxidants: Types and Characteristics
BHA: Butylated Hydroxyanisole
BHA is a phenolic antioxidant that inhibits oxidation of fats and fat-soluble nutrients such as vitamin A. Because it is fat-soluble and highly heat-stable, it is also used to prevent oxidation in baked and fried foods. It is cost-effective and provides strong antioxidant performance.
On the other hand, some animal studies have reported tumors in the stomach and bladder, and potential carcinogenicity has been discussed.
That said, the FDA recognizes BHA as generally safe when used at ≤0.02% of the fat content in food (about 200 ppm / 200 mg/kg). In pet food, safety is ensured by complying with permitted limits (in Japan, for example, the combined total of BHA, BHT, and ethoxyquin must be within 150 ppm).
BHT: Butylated Hydroxytoluene
BHT is also a phenolic antioxidant. Like BHA, it works by capturing free radicals that initiate oxidation and neutralizing them. It has similar heat stability to BHA and maintains its antioxidant effect even under high-temperature processing.
The European Food Safety Authority (EFSA) has evaluated BHT as safe for use in animal feed (including pet food) up to 150 mg/kg (150 ppm). At this level, it is rapidly metabolized and excreted, and accumulation in the body is not considered a concern.
However, some long-term animal studies have reported changes in liver enzymes and mild liver tissue changes at higher doses, and the effects of prolonged high exposure are not fully clarified. For this reason, strict compliance with legal limits and quality control testing of inclusion levels are important.
Ethoxyquin
Ethoxyquin is an organic nitrogen-based antioxidant that has also been used as an agricultural chemical. It is particularly effective at preventing oxidation of vitamin A and E, carotenoids, and other oxidation-sensitive compounds. It is also used to reduce the risk of spontaneous combustion in materials such as fish meal. Because its antioxidant effect is strong, it is used at very low inclusion rates (for humans in Japan, ADI = 0.0083 mg/kg body weight/day).
At the same time, concerns have been raised regarding carcinogenicity and genotoxicity based on findings such as positive results in chromosomal abnormality tests and signs suggesting bladder hyperplasia/tumor risk in chronic toxicity studies in rats.
Reflecting these concerns, Japan regulates ethoxyquin under the Pet Food Safety Act together with BHA and BHT: the combined total of BHA + BHT + ethoxyquin must be ≤150 ppm, and ethoxyquin itself is limited to ≤75 ppm in dog food and ≤150 ppm in cat food.
Natural Antioxidants: Types and Characteristics
Mixed Tocopherols (Vitamin E)
Mixed tocopherols are natural, fat-soluble antioxidants derived from vegetable oils, typically containing α-, β-, γ-, and δ-tocopherols. They interrupt oxidation chain reactions by donating hydrogen to free radicals. In pet food, they are widely used both for oxidative stability and as a vitamin E source. Among the tocopherols, γ- and δ-forms generally show stronger antioxidant activity.
Because they are naturally derived, consumer acceptance is high and safety is considered extremely strong. However, compared with synthetic antioxidants, they are less heat-stable and may degrade or be lost during high-temperature processes such as extrusion. They are also more expensive, and achieving the same oxidative protection as synthetic antioxidants may require higher inclusion levels or formulation support.
Rosemary Extract
Rosemary extract is a herb-derived antioxidant, mainly containing carnosic acid and carnosol, and is effective in suppressing lipid oxidation. It is frequently used in “natural” positioning and marketing claims.
However, because rosemary has a distinctive aroma and flavor, inclusion level must be carefully controlled in pet food applications. In addition, many components are volatile and relatively heat-sensitive, so effectiveness can decrease during thermal processing or long-term storage.
Ascorbic Acid (Vitamin C)
Ascorbic acid and vitamin C derivatives (water-soluble or fat-soluble forms) are sometimes used as antioxidants in pet food. Other ingredients—such as glutathione and selenium—may be included to support the body’s antioxidant systems, but the primary added antioxidants are typically the ones listed above.
Antioxidant Safety Standards and Regulations
| Antioxidant | Japan | United States | Europe |
|---|---|---|---|
| BHA (synthetic) | Total ≤150 ppm (BHA + BHT + ethoxyquin) | ≤0.02% of fat content (approx. 200 ppm) | 150 mg/kg |
| BHT (synthetic) | Total ≤150 ppm (BHA + BHT + ethoxyquin) | ≤0.02% of fat content (approx. 200 ppm) | 150 mg/kg |
| Ethoxyquin (synthetic) | Dogs: ≤75 ppm / Cats: ≤150 ppm (Total ≤150 ppm) | Max 150 ppm | Not permitted |
| Mixed tocopherols | No usage limit (subject to ingredient specifications and manufacturing standards) | No usage limit; GRAS recognized (must meet safety standards / certification) | No usage limit (approved as E306) |
| Rosemary extract | No usage limit (manufacturing standards apply) | No usage limit; GRAS recognized (must meet safety standards / certification) | Virtually no usage limit (approved as E392) |
Additives used in pet food are regulated under safety standards in each country. In Japan, the Act on Ensuring the Safety of Pet Food (Pet Food Safety Act) sets ingredient specifications. For example, the combined total of BHA, BHT, and ethoxyquin must be 150 ppm or less (and for dog food, ethoxyquin must be 75 ppm or less).
If these limits are exceeded, manufacture, import, and sale are prohibited. In the United States, under the AAFCO framework (FDA-related regulations), ethoxyquin is permitted up to 150 ppm in feed, and BHA and BHT are limited to 0.02% of the fat content (approximately 200 ppm).
In Europe (FEDIAF context), EFSA conducts similar safety assessments. For example, BHA and BHT are considered acceptable up to 150 mg/kg (150 ppm), while ethoxyquin is deemed not permitted. Under EU regulations, only authorized additives may be used, and manufacturers are required to comply with the relevant limits in each jurisdiction.
According to FEDIAF, both natural and synthetic preservatives/antioxidants are used within the permitted ranges under EU law, helping to prevent product deterioration and rancidity and enabling long-term shelf life.
Concerns About Synthetic Antioxidants vs. Scientific Assessment
Some pet owners believe that “BHA/BHT and ethoxyquin are carcinogenic or toxic and therefore harmful to pets.”
It is true that BHA has been reported in animal studies to increase stomach or bladder tumors, and the U.S. National Toxicology Program (NTP) has categorized it as a substance “reasonably anticipated to be a human carcinogen.” Ethoxyquin has also shown results in long-term rat studies suggesting abnormal bladder changes.
However, these studies typically used extremely high doses, and such results do not automatically mean the same risk occurs at the very low levels used in pet food.
In practice, authoritative risk assessments generally conclude that they are safe when used within regulated limits. EFSA has concluded that BHA is safe for relevant animal species up to 150 mg/kg, noting it is rapidly metabolized and excreted with no meaningful accumulation. Similarly, EFSA has assessed BHT as safe up to 150 mg/kg, reporting that potential transfer into edible animal products corresponds to only 1–3% of ADI, implying negligible consumer risk.
Ethoxyquin, however, is treated differently by region: it is not permitted in the EU, while the U.S. framework allows use up to 150 ppm.
A Risk-Based Perspective
The amounts pets and humans typically ingest are far below the doses used in studies where adverse effects were observed—often by tens of times or more. Regulatory bodies such as the FDA consider BHA/BHT generally safe within limits, and EFSA similarly concludes there is no consumer safety concern at permitted use levels.
BHA and BHT are metabolized in the body and excreted via urine and feces, and are not thought to accumulate significantly in tissues.
For ethoxyquin, Japan sets a very low ADI based on conservative safety factors from long-term data, and the permitted pet food inclusion levels are controlled to remain well below that threshold in practical use.
Overall, scientific evaluation supports safety under proper use and compliance.
Benefits and Limitations of Natural Antioxidants
Benefits of Natural Antioxidants
Natural antioxidants align well with premium and health-oriented market trends because consumers tend to trust “naturally derived” ingredients. Mixed tocopherols also add nutritional value as vitamin E, supporting antioxidant status in the body.
Plant-derived antioxidants such as rosemary extract can provide strong oxidation control, and in some cases may be combined with other antioxidants to achieve synergistic effects. Their toxicity and environmental risk are generally considered low, and their safety is widely accepted internationally.
Limitations of Natural Antioxidants
Natural antioxidants often do not match synthetic antioxidants in durability and stability. During extrusion or high-heat processing, or under long storage conditions, effectiveness may decline. For example, vitamin E losses during heat processing have been reported.
Natural ingredients can also show variability in supply and composition and are often more expensive. Achieving equivalent oxidative protection may require higher inclusion levels, careful combinations, or formulation adjustments.
Finally, “natural = safe” can be an oversimplification. Even vitamins can cause toxicity when excessively consumed (e.g., excessive vitamins A or E may cause adverse effects). Natural antioxidants are not “limitless” ingredients; they must also be used appropriately.
Consumer Misunderstandings and the Industry View
As demand for “additive-free” and “natural” products has increased, avoidance of synthetic antioxidants has become more common. The Consumer Affairs Agency of Japan has also expressed concern that consumers may overly stigmatize “artificial” additives, and has discussed reconsidering the use of terms such as “artificial” and “synthetic.”
From a marketing perspective, “No BHA/BHT” can be an effective selling point, and many manufacturers emphasize natural or additive-free positioning.
What Matters Most: Preventing Oxidation
From an industry standpoint, there is also a practical reality: if necessary antioxidants are not used, oxidation may progress and quality deterioration itself can harm pet health. Oxidized fats can cause off-odors, nutrient losses, and reduced palatability—making adequate oxidative protection essential.
In formulations containing oxidation-prone oils such as coconut oil or fish oil, shelf life can become significantly shorter without antioxidants.
In Japan, labeling regulations also require that the type and use of antioxidants be declared, allowing pet owners to confirm them on ingredient labels.
Additionally, some reported incidents such as pet seizure-like symptoms have been suggested in certain discussions to be linked not to ethoxyquin itself, but to highly oxidized oils (rancid fat toxicity). This is another reason simplistic conclusions like “synthetic antioxidants are always bad” can be misleading.
Scientifically, any antioxidant can be beneficial when used correctly at appropriate levels, and the burden on the body is considered extremely small under regulated use. At the same time, “natural is always safe” should not be overtrusted. The practical responsibility for the industry is to apply evidence-based decisions—using synthetic and/or natural antioxidants appropriately—to achieve both nutritional quality and safety.