Isostearic acid is a saturated fatty acid. Its structure makes it a great surfactant.

Surfactants help decrease the surface tension between two liquids. This property also makes it an effective emulsifier. Emulsifiers help prevent waters and oils from separating in a product.

Water. It's the most common cosmetic ingredient of all. You'll usually see it at the top of ingredient lists, meaning that it makes up the largest part of the product.

So why is it so popular? Water most often acts as a solvent - this means that it helps dissolve other ingredients into the formulation.