Polyols are alcohols containing two or more hydroxyl groups in their molecules. Their chemical and physical properties are similar to sucrose, but they are widely used in the food and pharmaceutical industries because of their lower calorific value (e.g., sorbitol, erythritol) and reduced cavities. Polyols also possess excellent hygroscopic and moisturizing properties (e.g., glycerin, butylene glycol), making them widely used in the cosmetics industry.

Alkanediols are alcohols containing two hydroxyl groups in their molecules. 1,2-Alkanediols have been widely used in the personal care industry, and their moisturizing and safety properties are generally accepted. They are also one of the commonly used additive-free preservatives in cosmetics. They exert their moisturizing effect by capturing water molecules through their hydrophilic groups, and also have a certain ability to inhibit bacteria and fungi.

The antibacterial ability of 1,2-Alkanediols increases with the length of their carbon chain. The most commonly used ones include 1,2-pentanediol, 1,2-hexanediol, and octyl glycol (1,2-octanediol). The water solubility of 1,2-Alkanediols decreases with the length of their carbon chain, and they may even become poorly soluble or insoluble in water. They also exhibit increased odor, decreased fluidity, and increased irritation. The antibacterial mechanism of alkanediols is that they can enter the cell membrane of microorganisms, disrupt the integrity of the cell membrane, allow cell fluid to leak out, and ultimately lead to the death of the microorganisms.

1,2-Pentanediol is a straight-chain alkyldiol with distinct polarity and non-polarity, giving it properties different from other diols. It can be used as a solvent, preservative, and moisturizer in many cosmetic raw materials.

1,2-Hexanediol exhibits good miscibility with other substances (easily soluble in water, ethanol, etc.), allowing it to combine well with other antimicrobial agents to achieve antibacterial and anti-allergic effects. Furthermore, it has been reported to be used in deodorants, showing significant deodorizing and antiperspirant effects on human skin while being gentle on the skin.

The order of antibacterial efficacy of alkyldiols from best to worst is: 1,2-Decanediol > Ethylhexylglycerin > 1,2-Octanediol (octylglycol) > 1,2-Hexanediol > 1,2-Pentanediol > 1,2-Butanediol > 1,2-Propanediol, 1,2-Ethylenediol. Among these, caprylyl glycol and ethylhexylglycerin have relatively good preservative effects, but adding too much can cause irritation and burning sensation. 1,2-pentanediol and 1,2-hexanediol are slightly milder, but their preservative effects are relatively poor (1,2-pentanediol has the worst preservative effect), and when added in large quantities, they leave a sticky residue on the skin. Therefore, when constructing a preservative-free system formulation, multiple preservative alternatives need to be used in combination.

These polyols all have some antibacterial effects, especially 1,2-nonanediol, 1,2-octanediol (caprylyl glycol), glyceryl monocaprylate, isooctylglycerin, and 1,2-hexanediol, which have strong antibacterial capabilities. 1,3-butanediol, 1,2-propanediol, 1,2-pentanediol, and glycerol (glycerin) have weaker antibacterial capabilities than caprylyl glycol and other polyols. It is worth noting that the antibacterial ability of diols increases with the number of carbon atoms, reaching its peak when there are about 6-8 carbon atoms. However, the antibacterial ability of diols decreases with the increase of carbon atoms, possibly because water solubility decreases with the increase of carbon atoms.