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 is one of the most abundant elements on Earth, found in sand, quartz and certain plants. This compound can be of natural origin or synthesised depending on the type of product desired. There are different types of silica, each with specific functions.

• Amorphous silica (INCI: Silica)

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

  In formulations, amorphous silica plays a multifunctional role. It is used as an absorbent due to its capacity to capture sebum and moisture, which gives it a mattifying effect particularly prized in treatments for oily skin. It also improves the sensory feel of creams and powders, imparting a soft, dry and velvety finish. Finally, it is used as a carrier for pigments in make-up products, promoting better dispersion and colour stability.

• Colloidal silica.

  This is a suspension of ultra-fine amorphous silica particles in water. When the silica is simply dispersed in water, without undergoing a complete chemical transformation, it does not convert into orthosilicic acid (Si(OH)₄) but remains amorphous, forming a stable suspension: this is colloidal silica.

  This 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 characterised by the presence of pores of extremely small diameter (< 2 nm) and a very high specific surface area (often exceeding 700 m²/g). This configuration gives it a strong adsorptive power, particularly for hydrophobic compounds such as lipids or odours.

  It is used in products requiring precise control of the skin shine, notably in treatments for oily skin prone to acne, long-lasting loose powders and certain aluminium salt-free deodorants. Thanks to its microporous structure, it acts as a carrier of lipophilic active agents, allowing their partial encapsulation, which can improve their stability or enable controlled release.

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

• Hydrated silica (INCI: Hydrated Silica)

  This precipitated form of silica is obtained by reacting sodium silicate with a strong acid. The resulting particles have an amorphous structure, are porous and exhibit controlled abrasiveness, making them particularly suitable for oral care products.

  It is predominantly used as a mild abrasive in toothpastes, allowing the removal of deposits without altering 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 ability to scatter light, hydrated silica can also play an opacifying role, improving the visual appearance of emulsions or cleansing gels.

Silica plays a multifunctional role owing to its physico-chemical properties, notably its porosity, high specific surface area and stability. Widely used in its amorphous form, silica primarily serves as an absorbent, mattifying, texturising 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’s surface. Microporous silica is best suited to this role thanks to its highly porous structure, with a large specific surface area, often > 500 m²/g. Its ability to capture lipids enables 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, notably their oil absorption capacity as well as their mattifying power. In the first graph, silica exhibits strong absorbing power, immediately after mesoporous magnesium carbonate, with approximately 1 g of oil absorbed per gram of powder. For comparison, other powders exhibit significantly lower values.

The second graph shows that silica exerts a significant immediate mattifying effect, exceeding 50% mattiness, but remains slightly less effective than kaolin and MMC. Finally, the last graph assesses the persistence of the mattifying effect over time. It can be seen that silica better retains its efficacy, with a decrease of approximately 20% after 8 hours, compared to 40% for MMC and 50% for kaolin.

However, these results should be interpreted with caution. The small number of participants (only 10 volunteers, or unspecified for certain tests) limits the statistical significance of the data.

In make-up, silica can thus be used in loose or compact powders, foundations and blushes for its mattifying, blurring effect and its ability to improve wear. In facial skincare, it is found in mattifying creams and 'oil-free' serums, where it regulates excess sebum while imparting a velvety feel. In hygiene products, it is incorporated into toothpastes for its gentle abrasive action, as well as into deodorants and cleansing gels for its absorbing power. It also features in hair care products, such as volumising powders or dry shampoos, where it absorbs oil at the roots and restores texture to the hair. Finally, in sun care products, silica contributes to the stabilisation of UV filters and to the improved dispersion of lipophilic phases.

According to several studies, the silica amorphous, regardless of its form, presents a good skin tolerance and does not significantly penetrate intact skin. A study ex vivo has shown that the amorphous silica used in cosmetics remains on the surface, without notable passage through the skin barrier and exhibits little or no irritation and cellular toxicity for amorphous particles ranging in size between 70 and 1,000 nm. The Cosmetic Ingredient Review considers the topical use of the silica as safe under customary conditions of use, excluding the inhalation of very fine dry powders.

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