Both in skincare and makeup products, CI 77491 is a very common ingredient in cosmetics. But what lies behind this "Colour Index"? We explain it here.
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What is "CI 77491" and what is its purpose?
Summary
Published November 5, 2021,
updated on November 27, 2024,
by
Stéphanie, PhD, Doctorate in Life and Health Sciences
—
5 min read
CI 77491: What Does It Do in a Cosmetic Formula?
Within the INCI system, the designation CI for "Colour Index" followed by 5 digits allows for the clear identification of colourants or pigments used in cosmetics.
Recognisable in INCI lists under the name "CI 77491", red iron oxide is a compound derived from minerals that belongs to a group of pigments called iron oxides, which are composed of oxygen and iron (68%). It is used as a dark red-brown pigment to add colour to cosmetic products.
Anecdote : Natural red iron oxide is rust.
At low concentrations, it is particularly found in the formulation of numerous tinted products (lipsticks, foundations, etc.) for its ability to impart a reddish or pinkish tone, whether to provide definition and depth to the formulations or to enhance the product's appearance.
Anecdote : Red iron oxide was once used to adorn the body and create prehistoric frescoes.
Red iron oxide is also often used in combination with other iron oxides, such as CI 77492 (yellow) and CI 77499 (black), to create shade ranges. Besides its colouring power, it also has the added benefit of providing the skin with enhanced protection against certain wavelengths of high-energy visible light, particularly attenuating visible blue light (between approximately 400 nm and 500 nm), which can also be harmful to the skin, through absorption and reflection.
| Characteristics | Values |
|---|---|
| Chemical Formula | Fe2O3 |
| Synonym | Red iron(III) oxide, anhydrous iron(III) oxide, anhydrous ferric oxide, iron sesquioxide, Indian red, red iron oxide, hematite |
| Appearance | Red-tinted powder |
| Method of Obtaining | Thermal decomposition, precipitation, and calcination of iron hydrates |
| Molar Mass | 159.69 g/mol |
| Solubility | Insoluble in water and organic solvents; Dispersible in fats and concentrated mineral acids |
| Stability | Stable |
"CI 77491" is primarily found in our tinted hybrid skincare products to pigment the formulations.
How is red ferric oxide produced?
First of all, the red iron oxide used in cosmetics is produced through laboratory synthesis to control quality and ensure it is free from impurities. Indeed, to be used, red iron(III) oxide must meet the purity criteria specified in the European Commission Directive 95/45/EC. Naturally occurring ferric oxide can contain impurities, such as chromium or other organic materials, which can be harmful to health and affect the quality of the pigment.
Purity conditions: No more than 1% of water-soluble substances, no more than 5 mg/kg of arsenic, no more than 50 mg/kg of barium, no more than 5 mg/kg of cadmium, no more than 100 mg/kg of chromium, no more than 50 mg/kg of copper, no more than 20 mg/kg of lead, no more than 1 mg/kg of mercury, no more than 200 mg/kg of mercury and no more than 100 mg/kg of fully dissolved zinc.
The synthesis of red pigment based on iron oxide is thus carried out industrially via the precipitation process (solutions of FeSO4 and NaOH), the Penniman-Zoph process (scrap iron) or the Laux process (solutions of iron (II) chloride or aluminium chloride, sulfuric acid, and phosphoric acid). The obtained pigments are then washed, dried, calcined, and ground.
What about the safety profile of CI 44791?
Synthetic red iron oxide is considered safe for use in skincare products. It is well tolerated by all skin types, including those with sensitive skin.
Sources
Commission Européenne. BREF Chimie inorganique de spécialité (2007).
BOLAND P. & al. Iron oxides in novel skin care formulations attenuate blue light for enhanced protection against skin damage. Journal of Cosmetic Dermatology (2021).
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