Polyols are molecules containing several alcohol functions (-OH) on their molecules, Diols contain 2 alcohol functions (-OH).
They are all known to help in the protection of cosmetic formulas against microbiological development and pollution. They work by promoting the penetration of preservatives into bacterial cell walls. They are not listed as preservatives in cosmetic regulations, so cannot be said “preservatives”. Their suppliers must claim another main property, otherwise cosmetic manufacturers would be blamed to use illegal preservatives.
The fact that they are not listed as preservatives is also a way for cosmetic manufacturer to claim “preservative free” : if a formula is only protected against microbiological organism thanks to polyols / diols, it indeed does not contain preservatives, in the sense of the law. This is a very common trick in the industry.
This family of molecule contains :
- Methylpropanediol : sold among others by Lyondellbasel under the tradename MPDIOL Glycol, it is claimed as main functionality to be an excellent solvent
and humectant. Methylpropanediol does not seen to have by itself very good preservative efficiency, but acts as a strong booster when associated to other molecules, like in Dr Straetmans Dermosoft OMP (blend of Methylpropanediol, Caprylyl Glycol and Phenylpropanol).