E-numbers / Other additives / E927a
also: ADA · E927a · the yoga mat chemical
A flour treatment agent banned in the UK and EU. It breaks down during baking into chemicals that raise carcinogenicity concerns in animal studies.
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Breaks down into semicarbazide, which caused tumours in animal studies and shows weak genotoxic activity, and into ethyl carbamate (urethane), classed by IARC as a probable human carcinogen.
Why it’s worth knowing. Breaks down into semicarbazide, which caused tumours in animal studies and shows weak genotoxic activity, and into ethyl carbamate (urethane), classed by IARC as a probable human carcinogen. Also a respiratory sensitiser in occupational settings.
Azodicarbonamide is a synthetic chemical compound used as a flour treatment agent and dough conditioner. It is a yellow-orange powder that acts simultaneously as a bleaching agent and a dough strengthener. It is not permitted as a food additive in the UK or EU.
When added to flour it oxidises the gluten proteins, strengthening the dough network, making it more elastic and easier to handle at scale. It also bleaches flour, turning it whiter. During baking in the presence of moisture, it decomposes rapidly, leaving behind breakdown products rather than remaining intact in the finished bread.
Not legally permitted in UK or EU food. Historically used in commercial bread, sandwich loaves, burger buns, and other yeast-leavened baked goods processed at scale. It is still permitted in the United States and Canada in flour at up to 45 ppm. On a US label it appears as azodicarbonamide or ADA in the ingredients list; there is no UK E number in active use.
When azodicarbonamide reacts with moist flour during mixing and baking, one of its main breakdown products is semicarbazide (aminourea). EFSA assessed semicarbazide and concluded it shows weak carcinogenic activity in laboratory animals and has weak genotoxic activity. Human epidemiological data on dietary semicarbazide are not available at meaningful levels because EU and UK exposure from this additive is eliminated by the ban.
Semicarbazide, a breakdown product of azodicarbonamide in baked goods, showed weak carcinogenic activity in animal studies and weak genotoxic activity in laboratory tests.
A second breakdown product is ethyl carbamate, commonly known as urethane. IARC classifies urethane as a Group 2A probable human carcinogen, based on sufficient evidence in animals and limited evidence in humans. Urethane forms in small quantities during baking at high temperatures and is also found naturally in fermented foods such as wine and bread, making the contribution from azodicarbonamide one source among several.
Ethyl carbamate (urethane), formed during baking from azodicarbonamide, is classified by IARC as a probable human carcinogen (Group 2A) based on sufficient animal evidence.
Occupational studies and WHO assessment link inhalation of azodicarbonamide dust in bakery and flour-milling workplaces to asthma, rhinitis and other respiratory sensitisation. The WHO noted in 1999 that the level of risk to consumers from residues in finished food is uncertain, but the occupational hazard for workers handling the powder directly is recognised. This concern is distinct from the carcinogenicity question and relates specifically to the intact compound before baking.
WHO linked workplace inhalation of azodicarbonamide to respiratory issues, allergies and asthma in workers; the compound acts as a respiratory sensitiser.
Because it is not permitted in UK food, direct exposure from UK products should not occur. Anyone buying imported US baked goods, or eating in US fast-food chains operating in the UK, should check the ingredient list for azodicarbonamide. People with asthma may wish to be aware of it as an occupational sensitiser in bakery settings.
The concern here is driven primarily by what happens to azodicarbonamide during baking, not the additive itself. The EU and UK took the precautionary step of not authorising it, rather than setting a limit, which is a stronger regulatory position than a mere ADI. The animal carcinogenicity signal for semicarbazide is real but weak, and human dietary evidence is absent by design (because the EU eliminated the exposure route). The IARC Group 2A classification for urethane is shared with red meat and various other dietary and environmental exposures, so context matters. The science is not settled on what dietary semicarbazide or urethane at baked-goods levels does to humans, but the EU's decision to prohibit the additive rather than quantify a safe limit reflects that the risk-benefit case for its use in food was not made.
Yes. Azodicarbonamide is not on the UK FSA approved-additives list and has no authorised E number for food use in the UK or EU. It is illegal to add it to food sold in the UK.
The EU did not authorise it as a food additive, in part because it breaks down during baking into semicarbazide, which showed weak carcinogenic and genotoxic activity in animal studies, and into urethane, an IARC Group 2A probable human carcinogen. The risk-benefit case for its use was not established to the regulator's satisfaction.
No UK or EU food should legally contain it. It may still be present in imported baked goods, burger buns, sandwich bread or rolls manufactured in the United States or Canada, where it remains permitted at up to 45 ppm in flour.
Azodicarbonamide is a synthetic chemical compound with no animal-derived ingredients, so it is vegan by composition. However, its dietary relevance in the UK is nil because it is not a permitted additive here.
Last reviewed: 20 June 2026
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