What is red iron oxide made of? Understanding its role in nutrition diet

November 10, 2025 •

3 min read

Over 40,000 years ago, natural iron oxides were used as pigments in prehistoric cave paintings. Today, many people wonder, what is red iron oxide made of, and how does this substance end up coloring food and dietary supplements?.

Quick Summary

Red iron oxide is essentially anhydrous iron(III) oxide ($Fe_2O_3$), found naturally as the mineral hematite or produced synthetically for greater purity. It functions as a non-nutritive colorant (E172) in many consumer products and is widely regulated for safe consumption.

Key Points

Chemical Formula: Red iron oxide is anhydrous iron(III) oxide with the chemical formula $Fe_2O_3$.
Natural vs. Synthetic: It exists naturally as the mineral hematite but is often produced synthetically for higher purity and color consistency.
Not a Nutrient: The iron in red iron oxide is not bioavailable and is not considered a nutritional source in the diet.
Food Additive (E172): In food and dietary supplements, it is used as a non-nutritive colorant under the European code E172.
Regulatory Approval: Food-grade red iron oxide is heavily regulated by agencies like the FDA and EFSA, which set strict purity standards for human consumption.
Primary Use: Its main purpose in food and supplements is to provide a consistent red color for visual appeal and product identification.
Safety Profile: When properly purified and used within regulated limits, it is considered safe, as it is poorly absorbed by the body.

What is red iron oxide? The chemical composition

Red iron oxide is an inorganic compound of iron and oxygen with the chemical formula $Fe_2O_3$. In its pure form, it is known as anhydrous iron(III) oxide. This compound gives many natural materials their red color. Red iron oxide used in food, supplements, cosmetics, and paints is specifically processed to ensure safety and consistent color.

The two sources: Natural vs. Synthetic

Red iron oxide can be sourced naturally or synthetically.

Natural Red Iron Oxide (Hematite): This form is the mineral hematite. While natural, it often contains impurities that must be removed for food-grade use. Historically used in art, synthetic versions are now preferred commercially for better consistency and purity.

Synthetic Red Iron Oxide: Produced through controlled chemical processes like the Penniman-Zoph method, synthetic red iron oxide offers high purity and consistent color. It is favored in food and pharmaceuticals for its purity, color control, tinting strength, and lack of heavy metal impurities found in natural ores.

Red iron oxide's role in nutrition and diet

Red iron oxide is not a source of dietary iron. It is used for its coloring properties, not its elemental iron content. The iron in red iron oxide is not efficiently absorbed by the body.

Use as a colorant (E172)

Approved as food additive E172 in the EU, red iron oxide provides red, brown, and pink hues in various products, including:

Tablet coatings: Provides color for capsules and pills.
Confectionery: Used in sweets and desserts.
Decorative coatings: Found on baked goods.
Cosmetics: Used in products like lipstick.

Safety and regulation of food-grade red iron oxide

Food-grade red iron oxide undergoes safety assessments and meets strict regulatory standards.

Regulatory approvals

FDA: The FDA approves specific iron oxides for use in drugs and cosmetics with strict purity standards.
EMA/EFSA: European agencies EMA and EFSA have approved its use in medicines and as food colorant E172 following safety evaluations.

Safety assessment

Studies show poor gastrointestinal absorption, with excess typically excreted. Food-grade red iron oxide is purified to remove toxic metals. Inhalation of iron oxide dust is a workplace hazard, necessitating safety guidelines.

Natural vs. Synthetic Red Iron Oxide: A Comparison


Aspect	Natural (Hematite)	Synthetic (E172)
Purity	Contains natural impurities, requiring refining.	High purity ($>$99% $Fe_2O_3$) due to manufacturing.
Color Consistency	Color varies with mineral source.	Highly consistent color batch-to-batch.
Tinting Strength	Lower tinting strength.	Higher tinting strength.
Impurities	Raw ore may contain heavy metals; requires purification.	Controlled process eliminates harmful impurities.
Cost-Effectiveness	Can be less expensive for some uses but hard to process consistently.	Cost-effective for large-scale production due to quality and lower usage.

Conclusion

Red iron oxide is the inorganic compound $Fe_2O_3$, found naturally as hematite or produced synthetically for purity and consistency. It serves as a food-safe colorant (E172) and is not a source of dietary iron. Its use in coloring foods and supplements is supported by regulatory approvals from bodies like the FDA and EFSA, ensuring high purity for consumption.

For more details on food additives and colorants, consult the European Food Safety Authority (EFSA) website.

Frequently Asked Questions

The main difference lies in their purity and consistency. Natural red iron oxide (hematite) is a mined mineral with impurities, while the synthetic version is manufactured in a controlled process to achieve very high purity, consistent color, and stronger tinting power.

No, red iron oxide is not a good source of dietary iron. The iron in the compound is not easily absorbed by the body. It is used as a colorant rather than a nutritional additive.

E172 is the European food additive code for iron oxides and hydroxides, including red, yellow, and black variants. It indicates that the substance is approved for use as a colorant in food products.

Yes, when used within regulated limits, food-grade red iron oxide is considered safe. Regulatory bodies like the FDA and EFSA set strict purity standards to ensure it is non-toxic and poorly absorbed by the body.

Synthetic iron oxide is used in tablets and capsules to provide consistent, vibrant color. This helps with product identification, brand recognition, and can improve patient adherence by making pills easier to distinguish.

Red iron oxide can be found in a variety of products, including coated tablets and capsules, some confectionery, certain decorative coatings on foods, and cosmetics like lipsticks and eyeshadows.

Red iron oxide has a similar chemical composition to rust, which is a hydrous ferric oxide. However, in chemistry, rust is a more ill-defined substance. The food-grade red iron oxide is a highly purified and controlled form of anhydrous iron(III) oxide ($Fe_2O_3$).