E172: Iron Oxides and Hydroxides

What is E172 (Iron Oxides and Hydroxides)?

Iron oxides and hydroxides (E172) are inorganic mineral pigments used to provide a range of colors from yellow through red, brown, and black in food applications. They are among the oldest pigments known to humanity, having been used in cave paintings for tens of thousands of years. In modern food use, they are valued for their heat stability, light stability, and wide color palette. The three main forms are:

• Yellow Iron Oxide (Fe₂O₃·H₂O / FeOOH): Yellow-orange tones
• Red Iron Oxide (Fe₂O₃): Red to brown tones
• Black Iron Oxide (Fe₃O₄): Black to dark brown tones

Source and Production

Iron oxides for food use are produced synthetically to ensure purity:

1. Starting Material: Iron salts (iron sulfate or iron chloride) dissolved in water 2. Precipitation: Controlled oxidation and precipitation produces iron oxide particles 3. Washing and Drying: Extensive purification removes heavy metal contaminants 4. Milling: Ground to fine particle sizes (micronized)
2. Quality Testing: Strict testing ensures food-grade purity, particularly for heavy metals

Natural iron oxides (ochres, siennas) exist but are rarely used in food due to impurity concerns.

Common Uses in Food

E172 is used in specific food applications where mineral-stable colors are needed:

• Confectionery sugar coatings (chocolate dragées, sugar shells)
• Olives (ripe black olives — iron gluconate E579 more common but oxides also used)
• Salmon and shrimp paste (pink/orange shades)
• Certain cheeses
• Biscuit and cake decorations
• Pet food (not human food)
• Pharmaceutical tablet coatings
• Cosmetics

Health and Safety

Safety Profile

• Low absorption: Iron oxides are poorly absorbed from the gastrointestinal tract — most passes through unchanged
• Long history of safe use: Used in food and pharmaceuticals for decades
• Iron contribution: The small amount absorbed can contribute to dietary iron intake
• Mineral stability: Unlike organic dyes, iron oxides don't break down into potentially reactive compounds

Potential Concerns

• Heavy metal contamination: The main safety concern historically was contamination with heavy metals (lead, mercury, arsenic). This is why food-grade iron oxides must meet strict purity specifications
• Excessive iron intake: In theory, very high consumption could contribute to iron overload in susceptible individuals (e.g., those with hemochromatosis), though food additive use levels make this unlikely
• Interactions with medications: As an iron compound, high doses could potentially interact with certain medications

Regulatory Status

• European Union: Approved as E172 for specific food categories only (not general use)
• United States: Approved by FDA for specific uses
• ADI: 0.5 mg/kg body weight/day (as iron from iron oxides and hydroxides)

Identification on Labels

May appear as:

• E172
• Iron oxides
• Iron hydroxides
• Yellow iron oxide
• Red iron oxide
• Black iron oxide
• CI Pigment Yellow 42 / Red 101 / Black 11

Conclusion

E172 (Iron Oxides and Hydroxides) are among the more stable and reliably safe inorganic food colorings. Their very low GI absorption, combined with tight regulatory purity requirements, means they present minimal risk to consumers at normal dietary exposure levels. Their heat and light stability make them practically useful in applications where organic colorings would degrade. For most consumers, they are a relatively low-concern food coloring, though those with iron metabolism disorders should be aware of their presence in highly colored confectionery products.