INCI name
Silica
Also listed as: Silicon dioxide, silica silylate (a related, treated form)
Silica in cosmetics is silicon dioxide. It can be a fine powder that gives a soft-focus, mattifying feel in primers and powders, or a thickener in toothpaste and gels. Silica silylate and silica dimethyl silylate are surface-treated grades with their own INCI names; they are not identical to plain silica.
Like other fine powders, loose silica can be dusty. In a cream or a pressed powder it is bound into the formula and is not used as a loose dust.