BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene) are synthetic antioxidants added to food to prevent fats and oils from going rancid. You’ll find them listed on ingredient labels of cereals, snack foods, chewing gum, and many other processed products that contain fat. They work by blocking the chemical reactions that cause fats to break down, which extends shelf life and keeps food from developing off flavors and odors. Both have been used in the food supply for decades, but their safety profile has drawn increasing scrutiny.
How BHA and BHT Prevent Spoilage
Fats and oils are unstable. When exposed to oxygen, they undergo a chain reaction called oxidation that produces compounds responsible for stale, rancid tastes. BHA and BHT are fat-soluble molecules that interrupt this chain reaction before it spreads. They essentially sacrifice themselves, reacting with oxygen so the fat molecules don’t have to. This is the same basic principle behind vitamin E (a natural antioxidant), but BHA and BHT are cheaper to produce and more stable at the high temperatures used in food manufacturing.
Because they dissolve in fat rather than water, both additives are used specifically in fatty or oily foods. They’re particularly common in products that sit on store shelves for weeks or months, where oxidation would otherwise degrade quality long before the product reaches your kitchen.
Foods That Commonly Contain Them
The FDA permits BHA and BHT in a range of products, each with specific concentration limits. Dry breakfast cereals can contain up to 50 parts per million (combined BHA and BHT). Potato flakes, dehydrated potato shreds, and sweet potato flakes are also capped at 50 ppm. Emulsion stabilizers used in shortenings can contain up to 200 ppm. Active dry yeast is allowed up to 1,000 ppm of BHA. Chewing gum base can contain either additive at up to 0.1 percent of the base.
Beyond these specific categories, you’ll commonly spot BHA and BHT in butter, lard, shortening, baked goods, fried snacks, instant noodles, and food packaging materials. BHT in particular is often added to cereal box liners and other packaging to prevent the fats in the food from oxidizing even before you open the package. If a product contains oil or fat and has a long shelf life, there’s a reasonable chance one or both of these additives are involved.
The Cancer Question
BHA carries the more serious flag. The International Agency for Research on Cancer classifies it as Group 2B, meaning “possibly carcinogenic to humans.” That classification is based on animal studies in which chronic dietary exposure to high levels of BHA caused benign and malignant tumors of the forestomach in rats of both sexes and in male mice and hamsters. The U.S. National Toxicology Program goes slightly further, listing BHA as “reasonably anticipated to be a human carcinogen” based on sufficient evidence from animal studies. A later study found that BHA fed to fish larvae caused liver cancer in the adult fish.
The catch is that humans don’t have a forestomach, which is the primary tumor site in rodents. And a population-based study within the Netherlands Cohort Study found no increase in stomach cancer risk at typical dietary intake levels of BHA. So the animal evidence is concerning, but it hasn’t translated into clear human risk at the doses people actually consume. The epidemiological data, however, remains limited. There simply haven’t been enough human studies to draw firm conclusions either way.
BHT’s cancer picture is murkier. Some studies in mice and rats found lung or liver tumors after oral BHT exposure, and there is some evidence BHT can promote lung cancers that were initiated by other agents. The European Food Safety Authority concluded that BHT is not a concern for genotoxicity (direct DNA damage) and that any cancer-causing potential would require a minimum threshold dose, meaning very low exposures likely pose no risk.
Effects on Hormones and Organs
BHT has raised concerns beyond cancer. In animal studies, repeated exposure caused changes in liver tissue in mice and rats, increased the relative weight of the thyroid and adrenal glands, and triggered signs of thyroid hyperactivity. These thyroid effects appear to stem from BHT revving up liver enzymes that break down thyroid hormones, forcing the thyroid to work harder to compensate.
There are also signs of endocrine disruption. One study using an immature rat model found that BHT decreased uterus weight, pointing to anti-estrogenic activity. In lab-based cell studies, BHT behaved as either a weak estrogen or an anti-estrogen depending on the cell type tested. European regulators have flagged the need for further evaluation of BHT’s effects on adrenal and thyroid function and its interactions with estrogen and androgen receptors.
Reproduction studies in rats identified effects on litter size, sex ratio, and pup weight gain during nursing. The lowest dose at which no adverse effects were observed in reproduction studies was 25 mg per kilogram of body weight per day, a level far above what humans typically consume but relevant for setting safety limits.
How Your Body Handles These Chemicals
Both BHA and BHT are fat-soluble, which means they can be stored in body fat. Research comparing levels in rats, monkeys, and humans found that BHT accumulates in fat tissue at roughly ten times the level of BHA on an equivalent dose basis. Neither compound shows progressive buildup over time, meaning your body does clear them, but not completely between exposures.
An interesting wrinkle: when BHA and BHT are consumed together (as they often are, since foods frequently contain both), BHA levels in fat tissue increase compared to consuming BHA alone. This interaction suggests the two chemicals influence each other’s metabolism. Analysis of Canadian human fat tissue samples found detectable levels of both compounds, at 0.01 ppm for BHA and 0.12 ppm for BHT, confirming that everyday dietary exposure does result in measurable tissue storage. On a dose-per-body-weight basis, accumulation in human fat tissue is greater than in rats, which complicates the use of rat studies to predict human safety margins.
Where Regulators Stand Today
The FDA classifies both BHA and BHT as Generally Recognized as Safe (GRAS) within the specified concentration limits for each food category. However, the FDA has placed both chemicals on its list of select food supply chemicals currently under review, signaling that reassessment is underway.
European authorities have set notably different safety thresholds. The EU’s Scientific Committee for Food set an acceptable daily intake for BHT at 0.05 mg per kilogram of body weight per day, six times lower than the limit set by the international JECFA panel (0.3 mg/kg). For a 150-pound person, the stricter EU limit works out to about 3.4 mg per day. That difference reflects disagreement about how much weight to give the thyroid and reproductive effects seen in animal studies.
Natural Alternatives Gaining Ground
Consumer demand for “clean label” products has pushed manufacturers toward natural antioxidant alternatives. Rosemary extract has emerged as the most promising replacement. In comparative studies, rosemary extract matched or outperformed synthetic antioxidants at preventing fat oxidation during deep frying, producing equivalent levels of oxidation byproducts across multiple measures. Tocopherols (forms of vitamin E) are another common natural option, though they tend to be less heat-stable than rosemary extract or synthetic antioxidants.
You’ll increasingly see “rosemary extract” or “mixed tocopherols” on ingredient labels where BHA or BHT once appeared, particularly in products marketed as natural or organic. These alternatives cost more and can sometimes affect flavor, which is why BHA and BHT remain widespread in conventional processed foods. If avoiding these synthetic antioxidants matters to you, checking ingredient labels is straightforward since both must be listed by name.