BHT
A synthetic antioxidant added to fats, oils and processed foods to stop them turning rancid and extend shelf life.
At high doses in animal studies, BHT promoted tumour growth in the lung, liver and thyroid. The same high-dose studies also affected litter size and pup weight across generations, which is why regulators set a strict daily intake limit.
What is it?
Butylated hydroxytoluene (BHT) is a synthetic phenolic antioxidant derived from petroleum chemistry. It is a fat-soluble, white crystalline solid that accumulates in body fat.
What does it do?
BHT scavenges free radicals that trigger oxidative chain reactions in fats and oils. By interrupting those reactions it prevents rancidity, off-flavours and colour changes in foods that contain fat.
Where you will see it
Vegetable oils, margarine, butter blends, crisps and snacks, biscuits, crackers, breakfast cereals, chewing gum, dried instant potato, and edible fats. Also used in food packaging materials where it can migrate into the food. On labels it appears as 'BHT', 'butylated hydroxytoluene' or 'E321'.
What the science says
Animal tumour promotion
In rodent studies at high doses, BHT promoted the development of tumours in the lung, liver and thyroid. Importantly, BHT is not genotoxic, meaning it does not directly damage DNA. Regulators conclude the tumour effect is a dose-threshold mechanism rather than an intrinsic cancer trigger, but the signal drove a conservative ADI. Human epidemiological data are sparse and do not establish a clear link at dietary exposure levels.
BHT at high doses promoted lung and liver tumours in rodents. EFSA concluded it is not genotoxic and that carcinogenic effects show a threshold mechanism.
The Norwegian Scientific Committee for Food Safety conducted a separate risk assessment and reached similar conclusions: BHT is a tumour promoter in animals at high doses, not a genotoxic carcinogen.
IARC classified BHT as Group 3: not classifiable as to its carcinogenicity to humans, reflecting inadequate evidence in humans and limited evidence in animals at relevant doses.
Reproductive and developmental effects
Two separate two-generation rodent studies found reduced litter sizes and lower pup body weights at doses well below those causing tumours. EFSA used these reproductive findings as the basis for setting the ADI, with a no-observed-adverse-effect level (NOAEL) of 25 mg/kg body weight per day and an uncertainty factor of 100. Whether these effects translate to humans at real dietary exposures is unknown.
Two-generation rodent studies showed reduced litter size and pup body weight at repeated BHT intake. EFSA derived its ADI of 0.25 mg/kg body weight per day from these studies using a NOAEL of 25 mg/kg bw/day and uncertainty factor of 100.
Endocrine activity
Some laboratory studies have observed weak hormonal activity for BHT, including weak oestrogenic and anti-androgenic signals. These are low-potency effects seen in cell and animal models. Regulatory bodies have not formally classified BHT as an endocrine disruptor under food additive law, but the signal is noted in the scientific literature.
BHT and its metabolites showed weak oestrogenic and anti-androgenic activity in in vitro reporter gene assays.
Where it stands with the regulators
Who should be careful
People managing hormonal conditions may wish to note the weak endocrine-activity signals in laboratory studies. Those with known sensitivity to phenolic antioxidants should check for 'BHT', 'butylated hydroxytoluene' or 'E321' on ingredient lists. BHT is found in a wide range of packaged and processed foods, particularly those with a long shelf life.
The honest read
BHT has been used in food for decades and regulators in the UK and EU have reviewed the evidence and kept it permitted. But the scientific picture is not uncomplicated: high-dose animal studies have shown tumour promotion in the lung, liver and thyroid, and reproductive effects across two generations. EFSA set a conservative daily intake limit based on those findings. IARC assessed BHT as Group 3, meaning the evidence in humans was inadequate to classify it either way. Weak oestrogenic and anti-androgenic signals have been observed in laboratory studies, though regulatory bodies have not yet formally acted on those. The honest read is that the animal signals are real and regulators took them seriously when setting limits. Whether typical dietary intakes reach levels that matter for human health remains genuinely uncertain.
Related additives
Common questions
Is E321 banned in the UK?
No. BHT is approved for use in the UK as a food antioxidant under the UK FSA approved-additives list and assimilated EU Regulation 1333/2008. It is permitted in specific food categories at defined maximum levels.
What do regulators make of BHT's animal cancer data?
EFSA and UK regulators reviewed the animal data and concluded the tumour-promotion effect has a dose threshold, meaning very high doses are needed to trigger it. They set a strict daily intake limit (0.25mg/kg body weight per day) and kept BHT permitted. IARC classified BHT as Group 3 in 1986, meaning the evidence was inadequate to classify it as a human carcinogen either way.
What foods contain E321?
BHT is most commonly found in edible fats and oils, margarine, crisps and snacks, biscuits, crackers, breakfast cereals, dried instant potato and chewing gum. It is also used in some food packaging materials from which it can migrate into food. Look for 'BHT', 'butylated hydroxytoluene' or 'E321' in the ingredients list.
Is E321 vegan?
Yes. BHT is a synthetic compound derived from petroleum chemistry and contains no animal-derived ingredients.
Sources
- EFSA ANS Panel: Re-evaluation of butylated hydroxytoluene BHT (E 321) as a food additive, EFSA Journal 2012;10(3):2588
- UK FSA Approved Additives and E Numbers
- Norwegian Scientific Committee for Food and Environment (VKM): Risk assessment of BHT
- IARC Monographs Vol. 40: Butylated Hydroxytoluene (BHT) summary and evaluation (inchem.org)
Aaron Keen is the founder of NutraSafe. He researches and writes every additive entry himself, from the primary sources. About the research →
This is a guide, not medical advice. If an additive affects you, speak to your GP or a dietitian.
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