How is the silica used in cosmetics extracted?

The most commonly used form in cosmetic formulations is precipitated silica, also known as synthetic amorphous silica. It is produced by a chemical reaction between sodium silicate and a strong acid, such as sulfuric or hydrochloric acid. This reaction, carried out in an aqueous medium under stirring, causes the precipitation of silica particles in the form of a gel or powder. The synthesis conditions (temperature, pH, reaction time) directly influence the particle size, porosity, and shape, allowing the production of grades tailored to various uses: thickeners, mattifiers, opacifiers, or texture agents. This form is highly purified and contains no crystalline silica. It is approved by regulatory bodies such as the EFSA or SCCS for non-inhalation cosmetic use.

The silica can also be obtained in colloidal, meaning dispersed in water at the nanoscale. This form is produced by the controlled polymerization of silicic acid in an aqueous medium. The process yields a stable suspension of spherical nanoparticles of amorphous silica, generally ranging from 5 to 100 nanometers in size. This colloidal form is primarily used as a texture stabilizer or to enhance the film-forming effect of certain gels or serums. However, its use in cosmetics is regulated due to concerns related to nanomaterials, particularly when they can penetrate the skin barrier or be inhaled. In topical application, these forms are considered safe as long as they are not used in aerosols or loose inhalable powders.

The various forms of silica used in cosmetics are regulated and assessed by European authorities. The Scientific Committee on Consumer Safety (SCCS) confirmed in 2015 that precipitated, hydrated or colloidal amorphous silica poses no health risk when used under the recommended conditions. However, the crystalline silica naturally present in sand or quartz is banned in cosmetic products due to its potential toxicity when inhaled.