Hexamethylene tetramine
A preservative that works by releasing formaldehyde. Permitted in the UK and EU only in Provolone cheese, at very low levels.
Hexamethylene tetramine releases formaldehyde when it breaks down in acidic conditions. Formaldehyde is classified by IARC as a Group 1 carcinogen, meaning it causes cancer in humans at sufficient exposure.
What is it?
Hexamethylene tetramine (also called hexamine or methenamine) is a synthetic cage-like molecule made by reacting formaldehyde with ammonia. It is a white crystalline solid, soluble in water, with a faintly sweet odour.
What does it do?
Under acidic conditions or heat, hexamethylene tetramine breaks down and releases formaldehyde. It is that released formaldehyde which kills bacteria, yeasts and moulds. The compound is used in certain aged cheeses where the rind or surface is briefly treated to control unwanted microbial growth during maturation.
Where you will see it
In the UK and EU, E239 is only authorised for use in Provolone cheese, an Italian semi-hard cow's milk cheese. Outside Europe it has historically been used in some preserved fish products and pickled foods, but those uses are not permitted here. On a UK or EU label it appears as 'hexamethylene tetramine' or 'E239'.
What the science says
Formaldehyde release and cancer risk
The antimicrobial action of E239 depends entirely on it releasing formaldehyde. Formaldehyde is a well-established human carcinogen, primarily linked to nasopharyngeal cancer and leukaemia in people with occupational exposure at high concentrations. In the food context the residual formaldehyde in treated cheese is very low and subject to a strict limit, but the association with a Group 1 carcinogen is the reason regulators have kept the permission narrow and refused to expand it.
Formaldehyde is classified as a Group 1 carcinogen by IARC, with sufficient evidence for nasopharyngeal cancer and strong evidence linking it to leukaemia.
EFSA's ANS Panel re-evaluated E239 in 2014 and set an ADI of 0.15 mg/kg body weight per day, expressing concern that any increase in permitted uses or in the maximum permitted level would require new toxicity data before it could be approved.
The antimicrobial activity of hexamethylene tetramine is attributed to the formaldehyde it releases on hydrolysis under acidic or thermal conditions; the compound itself has limited direct antimicrobial action.
Global bans and restricted status
Many countries do not permit E239 in food at all. Australia banned hexamine as a food preservative because of the formaldehyde concern. The EU and UK retain a narrow, legacy permission for Provolone only. This restricted footprint reflects ongoing regulatory caution rather than a settled view that the compound is unremarkable.
Hexamethylene tetramine is not permitted as a food additive in Australia, where food standards authorities concluded the formaldehyde-releasing mechanism posed an unacceptable risk.
In the EU and UK, E239 is authorised solely for Provolone cheese at a maximum residual level of 25 mg/kg, expressed as formaldehyde, under assimilated EU Regulation 1333/2008 (Annex II).
Where it stands with the regulators
Who should be careful
People who wish to minimise exposure to formaldehyde-releasing compounds may choose to avoid traditionally produced Provolone cheese. Look for 'hexamethylene tetramine' or 'E239' in the ingredients. Most other cheeses do not contain it.
The honest read
The practical exposure from a small amount of Provolone is very low: the permitted residual limit is 25 mg/kg expressed as formaldehyde, and typical serving sizes are small. EFSA concluded that the current narrow use in Provolone does not raise a concern at that level. What the 2014 EFSA opinion also made clear, however, is that this permission has not been stress-tested -- no new genotoxicity data has been generated, and the ADI rests on older studies. The fact that a Group 1 carcinogen is the active agent, even at low residual levels, is why regulators worldwide have either held the line or moved to ban it altogether. The science here is not settled in the way it is for, say, a simple salt or acid: the compound is permitted in a narrow window, under restraint, with regulators explicitly unwilling to expand that window.
Related additives
Common questions
Is E239 banned in the UK?
No, it is not banned in the UK, but it is restricted to one specific food: Provolone cheese. It is not permitted in any other UK or EU food product. Several countries outside Europe, including Australia, have banned it entirely.
Why does E239 concern regulators?
Because it works by releasing formaldehyde, a substance that IARC classifies as a Group 1 carcinogen, meaning it causes cancer in humans. EFSA set a numerical ADI in 2014 and stated that any expansion of its permitted uses would require new safety data. The EU and UK have kept the permission extremely narrow as a result.
What foods contain E239?
In the UK and EU, only Provolone cheese is authorised to contain E239. It is used to control surface microbial growth during maturation. Outside Europe, it has historically appeared in some preserved fish and pickled products, but those uses are not permitted here.
Is E239 vegan?
The additive itself is synthetically produced from formaldehyde and ammonia, so it does not derive from animal products. However, it is only authorised in Provolone cheese, which is an animal product. E239 as a standalone ingredient is vegan; the food it is used in is not.
Sources
- EFSA ANS Panel: Re-evaluation of hexamethylene tetramine (E 239) as a food additive, EFSA Journal 2014;12(6):3696
- IARC Monographs Volume 100F: Chemical Agents and Related Occupations (Formaldehyde, Group 1)
- IARC Agents Classified by the Monographs, Volumes 1-141 (Formaldehyde: Group 1, Vol 100F, 2012)
- UK FSA Approved Additives and E Numbers
- EU Food Additives Listing by E Number (Bryant Research / Reading Foodlaw)
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