(Dr. Iulia Mihai, DVM) BHA (Butylated Hydroxyanisole) and BHT (Butylated Hydroxytoluene) are two different antioxidants, approved for use in both animal and human food (such as frozen foods, ready-made soups, or potato chips). Their use is considered completely safe under current regulations. They prevent fats from oxidizing and help preserve the color, texture, and overall quality of the products they’re added to. However, opinions regarding their safety are divided.

In this article, you will learn what BHT and BHA are, whether they are safe in pet foods, why they are used in pet foods, and more.

What Are BHT and BHA? 

Butylated hydroxyanisole and butylated hydroxytoluene are closely related synthetic antioxidants used as preservatives in lipsticks and moisturizers, among other cosmetics. They are also widely used in the food and pet food industry as food preservatives.

Chemical composition and role as antioxidants

BHT

Butylated hydroxytoluene; 2,6-Di-tert-butyl-p-cresol; food additive: E 321

• It is an oxidizing agent that inhibits reactions favored by oxygen, thus avoiding oxidation and deterioration of ingredients.

• It is often used together with BHA.

• It is authorized as a food additive. BHT has been evaluated by several expert committees (European, American, and the Organization for Economic Co-operation and Development). In 2019, American experts (Cosmetic Ingredient Review) concluded, once again, that it is safe for use.

The available data do not support the idea that BHT has endocrine-disrupting effects. Although effects on the liver, kidneys, and thyroid have been observed at high oral doses, these results do not apply to exposure through cosmetics, as absorption through the skin is very low and systemic exposure is negligible. BHT was included in a European re-evaluation of 28 substances suspected of having endocrine activity, and the conclusion was that it is not an endocrine disruptor. The regulated concentrations allow its safe use for consumers. Regarding allergies, there is no evidence that BHT causes sensitization, so it is not considered an allergen in cosmetics.

BHA

Butylated Hydroxyanisole; Tert-butyl 4 Methoxyphenol; food additive: E 320

• It is an antioxidant agent that inhibits reactions favored by oxygen, thus avoiding oxidation and deterioration of ingredients.

• BHA has been classified as a possible carcinogen by the International Agency for Research on Cancer, but the studies that led to this classification were conducted on models that cannot be extrapolated to humans, and there is no evidence that BHA is carcinogenic to humans. With regard to reproductive toxicity or endocrine disrupting potential, current data are insufficient and further studies are ongoing. BHA is also approved as a food additive. In practice, BHA is rarely used in cosmetics, and the very low concentrations guarantee safe use for consumers.

• Studies show that dietary exposure to BHA has been shown to cause tumors in experimental animals, including benign and malignant forestomach tumors in rats, and in male mice and hamsters. In animals without a forestomach, such as dogs, pigs, and monkeys, exposure to BHA was associated with increased cell proliferation and hyperkeratosis in the lower esophagus. Additionally, a study in fish (hermaphroditic Rivulus marmoratus) found that BHA exposure during the larval stage led to liver cancer (hepatocellular carcinoma) in adulthood.

• BHA is generally recognized as safe for use in foods, when the total antioxidants do not exceed 0.02% of the fat or oil content. It is also permitted as a food additive for direct addition to foods intended for human consumption.

Common uses in pet foods, treats, and supplements

BHA and BHT are often used in dry pet food, treats, or supplements to prevent fat oxidation, maintaining freshness, flavor, and product stability. The EU regulations on BHA as a feed additive, implemented in 2020 for all animals except cats, and in 2022 specifically for cats, allow the combination of BHA with BHT in various animal feeds, with a maximum permitted level of 150 mg/kg. BHT, in turn, is assessed by experts as an effective and acceptable antioxidant for animal feeding, with no clear evidence of specific toxicity at normal doses. However, there are reservations about long-term safety: at high doses or in laboratory studies, toxic effects have been observed, including on the liver or by generating oxidative stress, which makes some owners prefer natural alternatives (e.g., tocopherols/vitamin E).

Sources of Exposure for Pets

Pets are exposed to BHA and BHT preservatives primarily through dry food, canned food, and processed treats. Dry dog and cat foods often contain fats and oils that can oxidize rapidly, and BHA and BHT are added to prevent rancidity and to maintain the flavor, color, and nutritional value of the product. Processed treats and snacks, which contain concentrated fats, can also be a significant source of exposure. Pet supplements, especially those rich in oils or vitamins sensitive to oxidation, may contain these antioxidants to ensure product stability and efficacy. As previously mentioned, typical levels of BHA and BHT in pet food are strictly regulated, with maximum limits around 150 mg/kg of complete food. Daily exposure depends on the type, amount, and frequency of food your pet consumes.

Health Concerns and Controversy in Pets 

BHA and BHT are commonly added to dog and cat food to prevent rancidity of fats and to maintain the freshness and flavor of the products. However, there is some controversy regarding the safety of these preservatives. Some studies in rodents have shown that BHA can cause stomach tumors, and BHT can damage the liver and kidneys when given in doses much higher than those found in regular dog and cat food. For this reason, some organizations have classified BHA as a possible carcinogen, although these conclusions cannot be directly extrapolated to dogs and cats, which have different metabolisms and distinct physiological responses. Furthermore, the possible long-term effects of BHA and BHT (e.g., oxidative stress or influences on the endocrine system) have also been discussed. However, current evidence does not support these risks at normal levels of use. To reduce any uncertainty, many dog and cat owners and even pet food manufacturers prefer natural alternatives, such as tocopherols or rosemary extracts, which contribute to food stability without exposing animals to BHA or BHT. 

Alternatives to BHT and BHA in Pet Products 

As mentioned earlier, pet food manufacturers and owners are looking for safer ways to keep their dog and cat food and treats fresh. Instead of synthetic preservatives (BHA and BHT), natural antioxidants are increasingly being used. Among the most commonly used are tocopherols or vitamin E, which protect fats from oxidation without affecting the flavor or nutritional value of the product. Rosemary extracts are also frequently added to pet food for their antioxidant effect and natural antibacterial properties. According to the ASPCA Animal Poison Control, rosemary does not pose a toxic risk to cats or dogs. However, keep in mind that large amounts of rosemary can lead to digestive upset, vomiting, nausea, diarrhea, or gastrointestinal irritation.

In addition to the use of these natural additives, there is a growing trend towards fresh and preservative-free products for pets. Refrigerated foods, ready-to-eat meals, and unprocessed treats allow for the reduction or even elimination of BHA and BHT, while providing a diet that is closer to natural and more appealing to pets. This shift addresses both long-term safety concerns and the demands of owners who want clean products with as natural ingredients as possible, without compromising on quality or freshness.

Iuliana graduated from the University of Agronomical Sciences and Veterinary Medicine in 2012, Romania. She has a Master’s degree in Small Animal and Equines Pathology and a strong affinity for Veterinary Parasitology and Laboratory. In 2013 she started her Ph.D. in epithelial cancer in dogs and cats. She volunteered at the faculty’s clinic in her 3rd year of study, and continued her career in small animal pathology and laboratory. She has one cat and eleven rats. Her interests outside of work include traveling, writing, and crafting.