also: Iron oxide red · CI Pigment Red 101 · Haematite-type pigment
A synthetic mineral pigment that gives food a red or reddish-brown colour. Used mainly on cake decorations, sugar-coated sweets, and supplement capsules.
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Red iron oxide tested positive for DNA damage in laboratory cell tests.
Why it’s worth knowing. Red iron oxide tested positive for DNA damage in laboratory cell tests. Regulators could not rule out genotoxicity because the toxicology evidence base was too thin to reach a conclusion, and most commercial supplies contain a substantial nano-sized particle fraction whose long-term behaviour in the gut is not well characterised.
Red iron oxide is an inorganic mineral pigment, chemically iron(III) oxide (Fe2O3), also known as ferric oxide. Food-grade versions are produced synthetically from iron salts under controlled conditions, rather than being mined, to achieve the purity required by food law. It is the same compound that gives natural red clay and rust their colour.
It acts purely as a colouring agent. The pigment is insoluble in water and stable under heat, light and acid, making it well suited to coatings and surface applications. Because it does not dissolve, very little iron is absorbed from it in the gut; most passes through the digestive tract unchanged.
Red iron oxide colours the hard coatings on sugar-coated confectionery and dragees, the outer shells of pharmaceutical and dietary supplement capsules and tablets, cake and dessert decorations, sausage casings, and sometimes the rind of certain cheeses. On a UK food label it appears as 'iron oxides and hydroxides' or 'colour (E172)' or 'colour (iron oxides)'.
When red iron oxide (and black iron oxide) were tested in mammalian cell cultures, they caused DNA strand breaks and formation of micronuclei, which are markers of genetic damage. These effects were seen in both nano-sized and larger particles. However, when red iron oxide was given orally to rats, no genotoxic effects were found in blood-forming cells. Because the two sets of results point in opposite directions and the testing database was incomplete, the EFSA Panel concluded it could not determine whether iron oxides pose a genotoxic risk.
Red and black iron oxide, in both nano and micro particle sizes, produced positive results in in vitro genotoxicity assays in mammalian cells, including DNA strand breaks and micronuclei induction.
In vivo oral administration of nano- and microsized red iron oxide did not elicit genotoxic effects in rat haemopoietic cells; however no in vivo data are available for the gastrointestinal tract, which is the site of direct contact.
When EFSA re-evaluated E172 in 2015, the panel found that the available biological and toxicological data were insufficient to carry out an adequate safety assessment. No new acceptable daily intake was set. The panel called for additional data on genotoxicity, carcinogenicity, and reproductive and developmental toxicity before a firm conclusion could be reached. This is a notable regulatory outcome: for most long-approved additives, EFSA reaches a positive conclusion; for E172, it explicitly could not.
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, and recommended additional toxicological data be provided.
No acceptable daily intake was allocated by EFSA in the 2015 re-evaluation. JECFA had previously set a group ADI of 0 to 0.5mg/kg body weight per day in 1980, but this was based on a much older and thinner dataset.
A 2020 study that characterised seven commercially available E172 samples found that more than 50% of particles in all samples had at least one dimension below 100 nanometres. Current EU and UK specifications for E172 do not require manufacturers to state particle size or the nano fraction. This matters because nano-sized particles can behave differently in the body from larger versions of the same material, and the 2015 EFSA opinion specifically flagged particle size as a data gap that needed to be addressed.
More than 50% of iron oxide particles detected in commercial E172 pigment samples fell in the nanoscale range (at least one external dimension 1 to 100nm), yet current regulatory specifications contain no particle-size requirements.
EFSA recommended that particle size and particle size distribution should be included in the specifications for E172, noting this information was absent from the submitted dossier.
Studies using simulated digestion show that iron oxide particles pass through the gastrointestinal tract without dissolving and are taken up only minimally into intestinal cells. Liver cells in culture showed greater interaction with iron oxide particles at high experimental concentrations, including changes in mitochondrial activity in some particle types, though no cell death was recorded at doses tested. These findings are from laboratory and cell culture models, not from human dietary exposure studies.
In artificial digestion models, iron oxide food colorant particles (E172) passed through without dissolving; only minor uptake into intestinal (Caco-2) cells was detected and negligible transport across the intestinal barrier.
At high experimental iron concentrations (100 to 200 micrograms Fe/mL), some iron oxide particle types impaired mitochondrial membrane potential in human liver (HepaRG) cells and triggered apoptosis signalling, though ATP levels remained stable and no significant cell death was observed.
There are no specific groups formally told to avoid E172 under UK or EU food law. People who wish to avoid food colour additives whose full safety review is unresolved can check labels for 'iron oxides and hydroxides', 'E172', or 'colour (E172)'. Parents of young children may note that EFSA's exposure modelling found toddlers reach estimated intakes up to 9.5mg/kg body weight per day at the 95th percentile in high-consumption scenarios, against a background of unresolved genotoxicity data.
Red iron oxide has been in food for many decades and is still permitted in the UK and EU. What makes it unusual among long-established additives is that the EU's food safety authority, after a formal re-evaluation in 2015, said plainly that it did not have enough toxicological data to complete an adequate safety assessment. That conclusion sits alongside positive laboratory results for DNA damage in cell cultures, and a 2020 finding that most commercial E172 products are substantially nano-sized, a characteristic not yet regulated. The in vivo animal data and the gut absorption models suggest limited real-world uptake. But the full toxicological picture, including carcinogenicity and reproductive studies, remains incomplete. The science is not settled.
No. Red iron oxide (E172, including the red sub-type) is an approved food additive in the UK under the assimilated EU Regulation 1333/2008. It appears on the UK FSA list of approved additives and E numbers. A claim that it is banned in Germany appears in some older reference sites, but no primary official source has been found to confirm a current national ban in any EU member state; this should be verified against the German Federal Office of Consumer Protection and Food Safety (BVL) directly.
In 2015, EFSA conducted a formal re-evaluation of E172 and concluded that the available toxicological data were insufficient to carry out an adequate safety assessment. The gaps included unresolved in vitro genotoxicity signals in red and black iron oxide, absence of carcinogenicity studies, and lack of reproductive toxicity data. EFSA called for additional studies to be submitted. The additive remains authorised while this process continues.
Red iron oxide is used mainly to colour the hard shells of sugar-coated sweets and dragees, the outer coatings of vitamin and supplement capsules and tablets, cake and dessert decorations, and sometimes sausage casings or cheese rinds. It is not typically used in everyday drinks or plain baked goods. On a label it appears as 'colour (E172)', 'iron oxides and hydroxides', or 'colour (iron oxides)'.
Yes. Red iron oxide is a synthetic inorganic mineral pigment with no animal-derived ingredients. It is suitable for vegans, vegetarians, and is generally considered kosher and halal, though individuals following specific dietary certification schemes should confirm with the product manufacturer.
Last reviewed: 20 June 2026
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