The Ingredients Nobody Explains to You.
TBHQ (tert-butylhydroquinone) is a synthetic antioxidant added to fats and oils to keep them from going rancid, which extends shelf life. US rules (21 CFR 172.185) allow it alone or together with BHA and BHT, as long as the total antioxidant content is no more than 0.02 percent of the food’s fat or oil content. The European Union permits it as E 319. The limit is a share of the fat, not of the food, so the more oil a product carries, the more TBHQ it can carry.
On a label it reads TBHQ, tertiary butylhydroquinone or tert-butylhydroquinone. These categories come from the National Toxicology Program’s 1997 report and the Environmental Working Group’s ingredient guide. Formulas change, so the ingredient list on the package in hand is the only record that counts.
The long-term studies did not find that TBHQ causes cancer. The US National Toxicology Program fed TBHQ to rats for up to 30 months and to mice for 2 years (Technical Report 459, 1997). Its conclusion was the same for male rats, female rats, male mice and female mice: “no evidence of carcinogenic activity” at 1,250, 2,500 or 5,000 parts per million in feed. That is about 50 to 240 milligrams per kilogram of body weight a day in the rats and 150 to 700 in the mice.
What did show up came at much higher doses. In a 13-week study, mice fed 10,000 parts per million or more, about 2,000 milligrams per kilogram of body weight a day and up, developed a thickened forestomach lining (mucosal hyperplasia, an increase in cell numbers, which is not a tumor). In cell tests TBHQ damaged chromosomes. In living animals the results conflicted, and the one test the European Food Safety Authority (EFSA) called conclusive, in mouse bone marrow, was negative.
There is one place in the record where tumors do appear. In experiments EFSA reviewed, rats were first dosed with known carcinogens and then fed TBHQ at 0.7 to 2 percent of the diet. In one of them TBHQ raised the number of benign growths (papillomas) in the esophagus and forestomach and lowered the number of colon cancers. In the bladder experiments EFSA described its promoting effect as weak. EFSA weighed all of it in 2004 and concluded that “TBHQ is not carcinogenic.”
The limit. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) set an acceptable daily intake of 0 to 0.7 milligrams per kilogram of body weight in 1997, and EFSA set the same figure in 2004. It comes from a long-term dog study in which blood changes appeared at 220 milligrams per kilogram and not at 72, with a 100-fold safety margin applied.
Where intake sits against that limit. JECFA’s 1998 intake review found that estimates built on the maximum levels in a draft international standard went over the limit for average intake in all three countries that supplied such data, while national estimates from four countries stayed under it. It concluded that “the potential exists for consumers of high levels of TBHQ to exceed the ADI,” and that it lacked the data to say how many consumers or by how much. EFSA’s 2016 exposure statement found the same pattern in Europe: with every permitted food assumed to carry the maximum, toddlers and children who eat the most went over the limit. With the levels industry and member states reported, no age group did.
The newer question is the immune system. Turley, Zagorski and Rockwell (Cytokine, 2015) exposed human blood immune cells to TBHQ in the laboratory at 0.1 to 5 micromolar and measured less of two signals that T cells release when activated, IL-2 and interferon gamma. Jin and colleagues from the same Michigan State University laboratory (Frontiers in Immunology, 2024) fed mice a diet containing 0.0014 percent TBHQ. Those mice made more allergy antibody (IgE) to a test protein applied to their skin, and had stronger anaphylaxis when they were later fed it. Naidenko and colleagues at the Environmental Working Group (International Journal of Environmental Research and Public Health, 2021) reported that TBHQ was active in immune-related tests in the US Environmental Protection Agency’s ToxCast screening data.
None of the three tested people eating TBHQ. Turley and colleagues wrote that “further studies will be needed to fully elucidate the effect of tBHQ on human immune responses.” An earlier immune study in mice, run for the National Toxicology Program and reviewed by EFSA in 2004, found only minor effects.
Correction, October 12, 2026. This entry used to say that at higher doses in animal studies TBHQ “caused stomach tumors and DNA damage.” In the long-term studies TBHQ on its own caused no tumors. The growths in the record came in rats first dosed with other carcinogens, as described above. It also credited the National Library of Medicine with symptoms at a 1 gram dose. That passage is in the Library’s record for hydroquinone, a different chemical, and is not in its record for TBHQ. Both lines are gone. The full account is on the corrections page.
Where Diet Discipline stands
TBHQ is on this list for one reason, and it is not cancer. The National Toxicology Program, JECFA and EFSA each examined that question and none found TBHQ carcinogenic.
It stays because of the arithmetic. The allowed intake is small, 0.7 milligrams per kilogram of body weight a day, and both JECFA and EFSA have shown on paper how intake passes it when many foods carry the permitted maximum, with toddlers and children first in EFSA’s numbers. The immune findings are early. They come from cells and mice, and they are reported here as that and no more. Diet Discipline counts an effect seen in animals at a dietary concentration as relevant to people until a human study says otherwise. That is a position, not a finding.
Set it against the purpose. TBHQ is not a nutrient. Its job is to keep oil from going rancid on a shelf. The frame to keep: a limit written as a percentage of the fat says little until you know how many of the day’s foods carry it.
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