Solubilizer

A solubiliser is an ingredient that lets a small amount of oil dissolve into a much larger amount of water, producing a clear liquid rather than a cloudy or separating one. It is the reason a transparent toner can carry a fragrance or a plant oil without visible droplets.

It works the way an emulsifier does — one end of the molecule is at home in oil, the other in water — but the ratio is different. An emulsifier holds two substantial phases together as a milky cream; a solubiliser handles a trace of oil in a water base and keeps the result see-through.

• Polysorbate 20 and PEG-40 hydrogenated castor oil are the two most commonly seen on labels.
• They appear in clear toners, mists, micellar waters and bi-phase removers.
• Because they help oil mix into water, the same chemistry also helps rinse oil away, which is why some turn up in cleansers.

A solubiliser has no action on skin and is not a quality signal in either direction. It is worth knowing chiefly to read a clear product's ingredient list correctly: the presence of an oil near the top of a transparent formula usually means a solubiliser is doing quiet work further down.