What it is
Silica is the chemical compound silicon dioxide (SiO2), built from silicon atoms each bonded to four oxygen atoms in a tetrahedral network, and found in nature as quartz and sand. In cosmetic formulas it is valued for its natural absorbency and light-diffusing properties, which help control oil and soften the look of fine lines and pores. The grades used in skincare and sunscreens are typically synthetic amorphous silica supplied as fine, porous spheres or powders. It also serves practical formulation roles such as thickening, anticaking, and helping suspend insoluble particles.
Safety & warnings
Amorphous silica used in cosmetics is generally well tolerated on skin and is widely incorporated into setting powders, oil-control products, and sunscreens. It is the crystalline form (such as respirable quartz dust) rather than the amorphous cosmetic grades that raises occupational inhalation concerns, which is a manufacturing handling issue rather than a finished-product topical one.
Origin & sourcing
Silica occurs abundantly in nature as quartz, sand, opal, and diatomaceous earth, but cosmetic grades are usually manufactured as synthetic amorphous silica. Precipitated silica is made by acidifying sodium silicate solutions to form a gel that is washed and dehydrated into a microporous powder, while fumed silica is produced by burning silicon tetrachloride in an oxygen-rich flame to create extremely fine particles. These amorphous forms are distinct from crystalline quartz.
History
Silicon dioxide has been known and used for millennia in the form of sand and quartz for glassmaking. The development of synthetic amorphous forms such as precipitated and fumed silica enabled the fine, controlled powders used in modern cosmetics, where silica is prized for absorbency and light diffusion.
Questions everyone asks
What does silica do in a sunscreen?
Silica absorbs oil and diffuses light, which helps give a smoother, more matte finish and can soften the appearance of pores; it also helps control the product's texture and suspend other ingredients.
Is the silica in skincare the same as sand?
Chemically both are silicon dioxide, but cosmetic silica is usually synthetic amorphous silica made as fine porous particles, which differs from the crystalline quartz that makes up most sand.
Is silica an active sunscreen ingredient?
No. Silica is not a UV filter. It is a texture and absorbency ingredient that supports the feel and finish of the formula.