also: Iron oxide yellow · Iron hydroxide yellow · CI Pigment Yellow 42
A mineral pigment used to add yellow and ochre tones to confectionery, cheese rinds, olives, and dietary supplements.
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EFSA concluded in 2015 that an adequate safety assessment of iron oxides could not be completed because the toxicological database was insufficient.
Why it’s worth knowing. EFSA concluded in 2015 that an adequate safety assessment of iron oxides could not be completed because the toxicological database was insufficient. No genotoxicity data exist for yellow iron oxide specifically, and regulators flagged that particle size specifications are missing, meaning the fraction of nanoscale particles in food-grade material remains unregulated.
Yellow iron oxide is an inorganic mineral pigment with the chemical formula FeO(OH), also known as goethite or hydrated iron(III) oxyhydroxide. Food-grade material is produced synthetically by precipitating iron(III) salts with an alkali, rather than being mined, to control purity. It is one of three iron oxide colours grouped under E172: yellow (E172b, also written E172iii), red (E172ii) and black (E172i).
It colours foods by absorbing specific wavelengths of light, producing shades from pale yellow to deep ochre. The pigment is insoluble, so it sits on or within the food matrix rather than dissolving. It is not absorbed to any meaningful degree by the gut wall and passes through largely unchanged. It does not supply nutritionally significant iron.
Yellow iron oxide is permitted for use in a range of foods at quantum satis (the amount sufficient for the colouring purpose): the rinds of hard cheeses, edible casings and coatings on meat products including sausages, table olives recoloured during processing, confectionery and sugar-coated items, cakes and dessert coatings, dietary supplement tablets and capsules, and some fish and shellfish pastes. On a UK label it will appear as 'E172', 'E172(iii)', 'iron oxides and hydroxides', or 'iron oxide yellow'.
When EFSA re-evaluated E172 in 2015, the Panel concluded that an adequate assessment of safety could not be carried out because there was not a sufficient biological and toxicological database. Key studies on carcinogenicity and reproductive or developmental toxicity existed but remained unpublished and could not be examined. This is not a finding of harm, but it is also not a finding of no harm: the data needed to answer the question were not available.
The EFSA ANS Panel concluded that 'an adequate assessment of the safety of E 172 could not be carried out because a sufficient biological and toxicological database was not available.'
Laboratory studies found that red and black iron oxides produced DNA strand breaks and micronuclei in mammalian cells, in both nano and micro particle sizes, which are signs of potential genetic damage. No genotoxicity studies have been done on yellow iron oxide specifically. EFSA stated that results from red iron oxide cannot be read across to yellow iron oxide because the two materials differ substantially in crystal structure, particle shape, and the fraction of nanoscale particles present.
Red and black iron oxide, in both nano and micro form, were positive in in vitro genotoxicity assays in mammalian cells, showing induction of DNA strand breaks and micronuclei.
No genotoxicity studies are available for yellow iron oxide (FeO(OH)), and EFSA stated that read-across from red iron oxide could not be performed due to marked differences in particle shape, size distribution, and nano-fraction.
EU rules for E172 do not specify any limit on particle size or the fraction of nanoscale particles. A 2020 study characterising seven commercial E172 products found nanoparticles in every sample examined, with four of five products having a median particle size below 100 nanometres. A 2026 study characterising twelve commercial samples confirmed each form contains a fraction of nanoparticles. EFSA recommended that particle size and distribution should be added to the specifications, but this recommendation had not been implemented in legislation as of the latest available information.
Nanoparticles were detected in all seven E172 products tested; four of five pigments analysed by electron microscopy had a median size below 100 nm. The study concluded consumers may be exposed to iron oxide nanoparticles through food pigments.
A characterisation of twelve commercial E172 materials identified four structural forms; each form contained a fraction of nanoparticles.
EFSA recommended that particle size and particle size distribution should be included in E172 specifications, noting the existing EU specifications do not limit the particle size or the fraction of nanoparticles.
In laboratory cell studies, iron oxide particles survived simulated digestion mostly undissolved and reached intestinal cells in particle form. Only minor uptake into intestinal cells was detected, with almost no onward transport. Liver cells took up substantially more material, and at high concentrations two particle types triggered markers of cell stress. These were high-dose laboratory findings and do not translate directly to real food exposures, but they suggest biological activity that has not been characterised in longer-term or in vivo studies.
Iron oxide particles passed gastrointestinal digestion largely intact; minor uptake occurred in intestinal cells but almost no transport beyond them. Liver cells showed 13 to 48 percent uptake depending on particle type, and two particles induced apoptosis markers at high concentrations.
A study of seven differently structured commercial E172 products during artificial digestion found particle dissolution was minimal and particles were taken up into intestinal cells to a minor degree, with limited transport across the intestinal barrier.
In a 28-day rat study, iron oxide nanoparticles at doses of 50, 100, and 200 milligrams per kilogram body weight per day altered the composition of gut bacteria in the gut contents. The high dose also affected bacteria living in the gut wall. Changes included decreases in Bifidobacterium and increases in other bacterial groups linked to metabolic and inflammatory pathways. These were very high doses by comparison with realistic food exposures and the study used isolated nanoparticles, not food-grade E172 directly.
In rats given 50, 100, or 200 mg/kg body weight per day of iron oxide nanoparticles for 28 days, all doses altered gut digesta microbiota composition and only the highest dose significantly changed mucosa-associated bacteria; decreases in Bifidobacterium and increases in Firmicutes were observed.
Because iron oxides are mineral-derived, the raw material can carry trace amounts of heavy metals including arsenic, lead, cadmium, and mercury. EFSA recommended that maximum limits for these elements be revised downward to ensure that food-grade iron oxides do not become a meaningful source of toxic element exposure. The current specifications in UK and EU law set limits but these are the same ones EFSA considered needed tightening.
The EFSA ANS Panel recommended revision of maximum limits for cadmium, arsenic, lead, and mercury in E172 specifications to ensure iron oxides applied as food additives are not a significant source of toxic elements.
There are no declarable allergens associated with yellow iron oxide. People avoiding mineral-derived additives may wish to check for 'E172', 'E172(iii)', or 'iron oxides and hydroxides' on the label. Vegans: synthetic iron oxides contain no animal-derived ingredients and are considered vegan.
Yellow iron oxide sits in an unusual regulatory position: it is permitted for use in food, yet the last full EFSA safety assessment concluded the available evidence was not sufficient to complete the evaluation. No genotoxicity studies have been done on yellow iron oxide specifically. For the related red and black forms, laboratory tests in mammalian cells showed signs of DNA damage, but EFSA said these results cannot be applied to yellow iron oxide because the materials differ. The nanoparticle question is genuinely open: commercial E172 products contain nanoscale particles, those particles survive digestion, and the specifications in law set no limit on them. Animal studies at high doses have shown gut bacteria changes, but doses were far above likely food exposure. None of this amounts to evidence that yellow iron oxide at food-use levels causes harm to people. It does mean that the safety file is incomplete, and regulators have said so plainly.
No. Yellow iron oxide (E172b, also written E172iii) is authorised in the UK under the assimilated EU Regulation 1333/2008, listed as Group II: food colours authorised at quantum satis. It has been confirmed as authorised on the UK FSA regulated products database with an authorisation date of 31 December 2020.
No. In its 2015 re-evaluation, EFSA's ANS Panel concluded that 'an adequate assessment of the safety of E 172 could not be carried out because a sufficient biological and toxicological database was not available.' Key studies on long-term effects were unpublished and could not be examined. This is a different outcome from a positive safety conclusion.
Yellow iron oxide is used in the rinds of hard cheeses, edible casings on sausages and meat products, table olives, confectionery and cake decorations, dietary supplement capsules and tablets, and some fish and shellfish pastes. On a label it appears as 'E172', 'E172(iii)', or 'iron oxides and hydroxides'.
Yes. Food-grade yellow iron oxide is produced synthetically from iron salts and contains no animal-derived ingredients.
Last reviewed: 20 June 2026
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