Propanediol 1,3 (referred to as Propanediol hereafter) is a natural, green, propylene glycol alternative derived from corn sugar, used as a humectant, hair and skin conditioner, preservative booster, and solvent with a light, non-sticky, slightly dry skin feel.

Propanediol may boost the efficacy of preservatives. Its efficacy was demonstrated when combined with preservatives containing phenoxyethanol against yeast, gram-positive, and gram-negative organisms, as well as mold.

0.25% Euxyl PE 9010 and 2% Propanediol proved effective against Pseudomonas aeruginosa (bacteria) and Aspergillus niger (mold), as well as at 4% against Staphylococcus aureus and Escherichia coli (bacteria) and 6% against Candida albicans (yeast).
Similar results were shown using 0.25% Optiphen with 2% against Staphylococcus aureus (gram-positive bacteria), Escherichia coli (gram-negative bacteria), and Aspergillus niger (mold), and Candida albicans (yeast) at 6%.
Reduced levels of Optiphen at 0.125% and 6% Propanediol were also shown to be effective.