Iron oxides are synthetic ingredients that function as colorants in cosmetics and personal care products. There are three basic shades: black (CI 77499), yellow (CI 77492) and red (CI 77491).
Iron oxides are inorganic compounds of iron and oxygen that have been used as coloring agents in cosmetics since the early 1900s. Iron oxides occur naturally, for example, rust is a type of iron oxide. Red iron oxide can be naturally derived from the mineral hematite; yellow iron oxides come from limonites such as ochers, siennas, and umbers; black iron oxide is obtained from the mineral magnetite. However, the iron oxides used in cosmetics are synthetic. There are a total of 16 different iron oxides used in cosmetics. In addition to use in cosmetics, iron oxides can be found in paints, coatings, and colored concretes.
Iron oxides are closely regulated by the United States Food and Drug Administration (FDA). The FDA’s Code of Federal Regulations for iron oxides states,“Synthetic iron oxides are produced in various ways, including thermal decomposition of iron salts, such as ferrous sulfate, to produce reds; precipitation to produce yellows, reds, browns, and blacks; and reduction of organic compounds by iron to produce yellows and blacks.”
In cosmetics and personal care products, iron oxides function as colorants. They are the main pigments used for matching skin tones in foundations, powders, concealers, and other make up for the face. Iron oxides can also be found in eye shadows, blushes, powders, lipstick, and mineral makeup. Iron oxides are available in three basic shades: black (CI 77499), yellow (CI 77492) and red (CI 77491). There are also various shades of brown iron oxides, but these are just mixtures of the three previously mentioned colors.
Yellow iron oxide (CI 77492) has the chemical formula Fe2O3•H2O. When yellow iron oxide is heated to about 800°C in the absence or limited supply of oxygen, it decomposes to form red iron oxide (Fe2O3). This process is known as calcination. Black iron oxide (Fe3O4) is a mixture of ferric and ferrous oxides.
Iron oxides are opaque and have excellent light stability, however, yellow and black iron oxides are sensitive to high temperatures. Iron oxides are also resistant to moisture, so they won’t easily bleed or smear. Iron oxides have excellent “staying power”, which means that the product will last for a long time without needing to be reapplied.
The Cosmetic Ingredient Review (CIR) Expert Panel has deferred evaluation of iron oxides because the safety has been assessed by FDA. All color additives used in foods, drugs, and cosmetics in the United States must be approved by FDA and listed in the Code of Federal Regulations. The FDA only approves colors after extensive review of all safety data and publication of the basis for its approval in the Federal Register.
Iron oxides are considered to be safe as used in cosmetics and personal care products because they are non-toxic and non-allergenic. Iron oxides are even well tolerated by those with sensitive skin. Even though iron oxides are synthetic ingredients, they are still often used in products that are marketed as natural or organic. This is because the synthetic versions of iron oxides are actually safer than the natural versions, which often contain impurities. For instance, oxides formed in a natural, uncontrolled setting are often contaminated with heavy metals. This demonstrates that just because an ingredient is natural does not always mean it is safe.
References: Wikipedia “Iron oxide”, Medium.com “The world of colors in cosmetics”, Chemists Corner “Iron Oxide Pigments in Cosmetics”, Cosmetics Info “Iron oxides”