E-numbers / Thickeners & emulsifiers / E431
also: PEG-40 stearate · Polyoxyl 40 stearate · Polyethylene glycol 2000 monostearate
A synthetic emulsifier made by bonding stearic acid with polyethylene glycol, used to help fat and water mix in processed foods.
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Animal studies on closely related emulsifiers in the same chemical family show disruption to gut bacteria and increased gut wall permeability.
Why it’s worth knowing. Animal studies on closely related emulsifiers in the same chemical family show disruption to gut bacteria and increased gut wall permeability. E431 itself has been studied far less than its relatives, and EFSA has flagged this data gap.
Polyoxyethylene 40 stearate is a synthetic non-ionic surfactant made by reacting stearic acid (a saturated fatty acid) with polyethylene glycol. The number 40 refers to the average number of ethylene oxide units in the polyethylene glycol chain. It is not found naturally in food.
It acts as an emulsifier and stabiliser: the stearic acid end is attracted to fats, the polyethylene glycol chain is attracted to water, and the molecule sits at the fat-water interface to stop them separating. It also improves texture and helps distribute fat-soluble vitamins and flavours evenly through a product.
Used in a narrow range of products including fine bakery wares, chewing gum, dietary supplement tablet coatings, vitamin and mineral preparations, and some flavouring emulsions. On a UK ingredient label it appears as E431 or as polyoxyethylene (40) stearate.
E431 belongs to the same chemical family as polysorbate 80 (E433) and other polysorbates. Animal studies on polysorbate 80 showed that chronic dietary exposure altered gut bacterial composition, reduced the protective mucus layer, and promoted low-grade gut inflammation. These effects have not been demonstrated in human trials at typical food-use doses, and E431 has been studied considerably less than polysorbate 80. The relevance to real-world exposure remains uncertain.
Dietary polysorbate 80 and carboxymethylcellulose at concentrations of 1% in drinking water induced low-grade inflammation, metabolic syndrome features, and altered gut microbiota composition in mice.
EFSA's re-evaluation of polysorbates (E432-E436) concluded that available data were insufficient to establish an ADI or to fully characterise risks to gut microbiota; the panel called for new toxicological studies.
E431 has fewer independent toxicological studies than the polysorbate group. EFSA has noted across this emulsifier class that older safety data predates modern gut-microbiome methodology. Because E431 is used in lower-volume applications than polysorbate 80, it has attracted less research attention. This absence of data is not the same as a clean bill of health.
The UK FSA authorises E431 under assimilated EU Regulation 1333/2008 (Annex II and III), reflecting the pre-Brexit adoption of existing EU permissions, with no new post-2020 re-evaluation of E431 independently published.
No specific population has been identified as clinically at-risk from E431 at typical dietary exposure. People with inflammatory bowel conditions who are monitoring emulsifier intake may wish to check labels for E431 or polyoxyethylene (40) stearate, given the class-level animal signals, but no clinical guidance mandates avoidance.
E431 sits in a scientific grey zone. The additive itself has been studied relatively little. The strongest concern signals come from animal research on its chemical relatives (particularly polysorbate 80), where gut-barrier disruption was observed at high doses. EFSA acknowledged in 2020 that the whole polysorbate-and-related-emulsifier class lacks modern gut-microbiome data, and called for new studies. No human clinical trial has demonstrated harm from E431 at food-use doses. At the same time, the regulatory permissions predate the gut-microbiome research era. The science here is genuinely unsettled.
No. E431 is authorised in the UK under the assimilated EU Regulation 1333/2008. It appears on the UK FSA's official register of approved food additives.
They are in the same broad chemical family of polyoxyethylene-based emulsifiers but are structurally distinct. Polysorbate 80 is made from sorbitol and oleic acid; E431 is made from stearic acid without the sorbitol base. Most of the published gut-microbiome research concerns polysorbate 80, not E431 directly.
E431 appears in a narrow range of products: some fine bakery wares, chewing gum, and tablet-coated dietary supplements or vitamin preparations. It is not a widely used emulsifier compared with lecithin or polysorbate 80. Look for E431 or polyoxyethylene (40) stearate in the ingredients list.
E431 is synthesised from stearic acid, which can be derived from either animal fats (tallow) or vegetable oils. The source varies by manufacturer. It is not automatically vegan, and products certified vegan will have used a plant-based stearic acid source. If this matters to you, check with the food manufacturer directly.
Last reviewed: 20 June 2026
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