Silica: what do you need to know about this mineral element?

The silica or silicon dioxide (SiO2) is a naturally occurring mineral in the Earth’s crust and represents one of the most abundant elements on Earth, found in sand, quartz, or certain plants. This compound can be of natural origin or synthesized depending on the type of products desired. There are different types of silica, each with specific functions.

• Amorphous silica (INCI: Silica)

  It is the form most commonly used in cosmetics. Structurally, it differs from crystalline silica by the absence of a regular atomic arrangement. This amorphous form is generally produced by precipitation or pyrogenation from sodium silicate. It exhibits a good skin tolerance and is not considered hazardous, provided it is not inhaled in its dry form.

  In formulation, amorphous silica serves a multifunctional role. It is employed as an absorbing agent due to its capacity to capture sebum and moisture, which imparts a mattifying effect highly sought after in skincare for oily skin. It also enhances the sensory texture of creams and powders, providing a soft, dry, and velvety finish. Lastly, it is used as a pigment support in makeup products, improving color dispersion and stability.

• Colloidal silica.

  This is a suspension of very fine amorphous silica particles in water. When silica is simply dispersed in water, without undergoing full chemical conversion, it does not convert into orthosilicic acid (Si(OH)₄) but remains in an amorphous form, forming a stable suspension: this is colloidal silica.

  The latter exhibits low bioavailability, meaning it is poorly absorbed by the body, as shown in the diagram. Indeed, only a small fraction can potentially be converted into orthosilicic acid under certain physiological conditions.

• Microporous silica.

  This highly structured form of amorphous silica is characterized by the presence of pores of very small diameter (< 2 nm) and a very high specific surface area (often exceeding 700 m²/g). This configuration imparts a strong adsorption capacity, particularly for hydrophobic compounds such as lipids or odors.

  It is used in products requiring precise control of skin shine, notably treatments for oily skin with acne-prone tendencies, long-wear loose powders, and certain aluminum salt-free deodorants. Thanks to its microporous structure, it acts as a carrier for lipophilic active ingredients, enabling their partial encapsulation, which can improve their stability or allow controlled release.

  Microporous silica is not considered a nanomaterial, since its primary particles exceed 100 nm and it does not penetrate the deeper layers of the skin. It is therefore deemed safe for topical cosmetic use based on the available toxicological data.

• Hydrated silica (INCI: Hydrated Silica)

  This precipitated form of silica is produced by reacting sodium silicate with a strong acid. The resulting amorphous particles are porous and exhibit controlled abrasivity, making them particularly well suited for oral care products.

  It is primarily used as a gentle abrasive agent in toothpaste, enabling the removal of deposits without compromising tooth enamel. It is also found in mechanical scrubs for the face or body, where it acts as a non-irritating physical exfoliant. Thanks to its light-scattering ability, hydrated silica can also serve as an opacifying agent, enhancing the visual appearance of cleansing emulsions or gels.

Silica plays a multifunctional role due to its physico-chemical properties, notably its porosity, high specific surface area, and stability. Widely used in its amorphous form, silica acts primarily as an absorbent, mattifying, texturizing, or even exfoliating agent, depending on its form (hydrated, colloidal, microporous, etc.). One of its main functions is to absorb excess sebum and moisture from the skin surface. Microporous silica is best suited for this role thanks to its highly porous structure, with a large specific surface area, often > 500 m²/g. Its ability to trap lipids allows it to mattify the skin.

A study aimed to compare the properties of various cosmetic powders with those of mesoporous magnesium carbonate (MMC). Several parameters were assessed, including their oil absorption capacity as well as their matting ability. In the first chart, it can be seen that silica exhibits a strong absorbing power, just after mesoporous magnesium carbonate, with about 1 g of oil absorbed per gram of powder. By comparison, other powders show significantly lower values.

The second graph shows that silica exerts a significant immediate mattifying effect, exceeding 50% mattification, while remaining slightly less effective than kaolin and MMC. Finally, the last graph evaluates the persistence of the mattifying effect over time. It appears that silica retains its efficacy better, with about a 20% decrease after 8 hours, compared to 40% for MMC and 50% for kaolin.