EXCIPIENT ⎪ SOLVENT
This is water, which is essential for dissolving other substances and emulsifying cosmetics.
There is a strong trend today to advocate reconstituted dry cosmetics, but it is not always easy to guarantee the same organoleptic qualities by reconstituting a powder with water afterwards. Dry formulations contain more surfactants, molecules that make textures more solid but which can potentially irritate the skin and scalp.
So water still has its place in cosmetic formulation!