Isobutane
A hydrocarbon gas used as a propellant to push oil or other products out of pressurised spray cans. The gas itself evaporates before it reaches your food.
What is it?
Isobutane is a colourless, odourless, flammable hydrocarbon gas (chemical formula C4H10) and the branched-chain form of butane. At room temperature it is a gas; it is stored under pressure as a liquid inside aerosol canisters.
What does it do?
As a propellant, isobutane builds pressure inside a sealed canister and expels the contents when the nozzle is opened. Because isobutane is a gas at ambient temperatures it evaporates essentially completely as the spray leaves the nozzle, so little or none remains in the food that lands on the pan or baking sheet.
Where you will see it
In the UK, E943b is approved only for use in vegetable oil pan sprays intended for professional catering and in water-based emulsion sprays, and at very low residual levels in food colour preparations. Most shoppers encounter it via catering-grade non-stick cooking spray used in commercial kitchens rather than consumer supermarket products. On a label it appears as 'isobutane' or 'E943b' in the ingredients list.
What the science says
What happens to isobutane once it leaves the spray can
Isobutane is a gas at room temperature and evaporates almost instantly on contact with air or a warm pan surface. Studies measuring hydrocarbon residues on food after cooking sprays are used have found total hydrocarbons well below 0.1mg per kg of cooked food, often substantially lower. The EU's Scientific Committee on Food reviewed residue data for propane, butane and isobutane in oil aerosol sprays and concluded exposure from this route is very low. EFSA's 2025 re-evaluation reached the same conclusion and said a quantitative exposure assessment was not needed given the gases' physical properties.
EFSA's Panel on Food Additives and Flavourings concluded that dietary exposure to isobutane from its permitted food uses is very low, based on the gas evaporating rapidly from food at ambient temperatures.
The EU Scientific Committee on Food reviewed residue data for propane, butane and isobutane in edible oil aerosol sprays and found total hydrocarbon residues in prepared foods below 0.1mg/kg, with most measurements substantially lower.
The 1,3-butadiene impurity
Manufacturing isobutane can leave trace amounts of 1,3-butadiene as an impurity. 1,3-Butadiene is classified by IARC as a Group 1 carcinogen, meaning there is sufficient evidence it causes cancer in humans, based on studies of workers in the styrene-butadiene rubber industry who developed leukaemia. EU and UK specifications for E943b cap 1,3-butadiene at no more than 0.1% by volume. EFSA's 2025 opinion noted that because dietary exposure to E943b is itself very low, the 1,3-butadiene contributed via food is considered negligible. However, EFSA also flagged a data gap: because information on manufacturing processes is limited, other unlisted impurities cannot be fully ruled out.
1,3-Butadiene is classified as carcinogenic to humans (Group 1) on the basis of sufficient evidence from occupational studies showing excess leukaemia in rubber-industry workers with a dose-response relationship, and carcinogenicity at multiple organ sites in rodents.
EU specifications for E943b permit a maximum of 0.1% v/v 1,3-butadiene as an impurity. EFSA noted uncertainties remain about other impurities due to limited information on manufacturing processes.
No ADI established
Neither EFSA nor the Joint FAO/WHO Expert Committee on Food Additives (JECFA) has set a numerical Acceptable Daily Intake for isobutane. Both bodies concluded that, given how little reaches food and how rapidly it evaporates, establishing a specific intake limit is not necessary. This absence of a numerical ADI reflects the very restricted conditions of use rather than a gap in the assessment.
JECFA previously determined that ADIs for butane, isobutane and propane were not necessary due to limited dietary exposure from their permitted food uses.
Where it stands with the regulators
Who should be careful
No specific population group is identified as needing to avoid E943b. The additive is not derived from animal products and presents no known allergen concern. Anyone who wants to minimise exposure from aerosol cooking products can use bottled oil instead of cooking sprays.
The honest read
Isobutane has one of the most straightforward profiles of any approved food additive: it is a gas that evaporates before it gets into your food, and both the 1999 EU committee and EFSA's 2025 re-evaluation found nothing in the residue data to prompt concern at the levels reaching food. The one genuine footnote is the 1,3-butadiene impurity, which is a known carcinogen at occupational inhalation levels, is capped in specifications, and whose contribution via food exposure is considered negligible by EFSA. The data gap EFSA flagged, about other possible impurities from manufacturing processes not currently listed in specifications, is a real uncertainty, even if a small one at these exposure levels.
Related additives
Common questions
Is E943b banned in the UK?
No. E943b is on the UK FSA approved-additives list and is permitted under assimilated EU Regulation (EC) No 1333/2008. Its use is restricted to vegetable oil pan sprays for professional catering, water-based emulsion sprays, and food colour preparations at low residual levels.
What is the 1,3-butadiene link?
1,3-Butadiene is a carcinogen classified IARC Group 1, meaning it causes cancer in humans, based on studies of workers exposed to it in industrial settings via inhalation. It can appear as a trace impurity in isobutane during manufacturing. EU and UK specifications limit it to no more than 0.1% by volume in E943b. EFSA's 2025 review concluded the amount of 1,3-butadiene reaching food via permitted uses of isobutane is negligible.
What foods contain E943b?
In the UK, E943b is restricted to vegetable oil pan sprays for professional catering use and water-based emulsion sprays. It is not permitted as an ingredient in typical consumer packaged foods. Most shoppers are unlikely to encounter it directly; it is primarily used in commercial kitchens. Where it does appear on a label, it will be listed as 'isobutane' or 'E943b'.
Is E943b vegan?
Yes. Isobutane is a hydrocarbon gas with no animal-derived origin. It is acceptable for vegans and vegetarians and carries no religious dietary restrictions.
Sources
- EFSA Panel on Food Additives and Flavourings: Re-evaluation of butane (E 943a), isobutane (E 943b) and propane (E 944) as food additives. EFSA Journal 2025;23(1):9203
- Re-evaluation of butane (E 943a), isobutane (E 943b) and propane (E 944) as food additives (PubMed/PMC)
- EFSA: Safety assessment of the substance isobutane, for use in food contact materials. EFSA Journal 2018;16(1):5116
- IARC Monographs Volume 97: 1,3-Butadiene, Ethylene Oxide and Vinyl Halides (2008)
- UK FSA: Approved additives and E numbers
- EU Scientific Committee on Food: Opinion on propane, butane and iso-butane as propellants (1999)
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