The moisturizing and preservative effects of caprylyl glycol (1,2-octanediol) in cosmetics

Caprylyl glycol, also known as 1,2-octanediol or octanediol, with the chemical formula C8H18O2, is a colorless liquid or white solid with a high melting point (36-38℃) and boiling point (131-132℃/10 mmHg). It is stable under normal temperature and pressure. Furthermore, octanediol has two hydroxyl groups, making it highly miscible with many other chemical substances and exhibiting good compatibility.

Caprylyl glycol is both a good humectant and an antibacterial agent, acting as a skin regulator. It moisturizes and softens the skin, providing a gentle preservative effect, and is therefore frequently added to cosmetics as a humectant or antibacterial agent. Caprylyl glycol can also be used in bath shampoos as a thickener and foam stabilizer.

The preservative effect of caprylyl glycol in cosmetics is primarily based on its unique antibacterial mechanism. First, caprylyl glycol can disrupt the cell membrane structure of microorganisms, causing leakage of cell contents and thus inactivating the microorganisms. Second, caprylyl glycol can inhibit the respiration and energy metabolism processes of microorganisms, further weakening their survival ability. In addition, caprylyl glycol also has certain moisturizing properties, forming a protective film in cosmetics to prevent the invasion and reproduction of microorganisms.

The antibacterial ability of diols increases with the number of carbon atoms, reaching its peak at around 6-8 carbon atoms. Then, with further increases in carbon atoms, the antibacterial ability of diols decreases, possibly due to decreased water solubility with increasing carbon atoms. Zhang Congcong et al. also studied the antibacterial efficacy of the moisturizing preservative caprylyl glycol.

Caprylyl glycol has antibacterial activity, with varying minimum inhibitory concentrations (MICs) against different bacterial species. The inhibitory concentration against *Escherichia coli* and *Candida albicans* was 8 mg/ml, while the inhibitory concentration against *Staphylococcus aureus*, *Pseudomonas aeruginosa*, and *Aspergillus niger* was 16 mg/ml.

The dosage and antibacterial effects of 1,2-hexanediol, 1,2-caprylyl glycol (caprylyl glycol), glyceryl monocaprylate, and isooctylglycerol were tested. Using a facial mask liquid as a base, the antibacterial effects of adding different concentrations were tested, and the results are shown in Table 3: The antibacterial ability increased with increasing dosage. 1,2-hexanediol, glyceryl monocaprylate, and isooctylglycerol all passed bacterial and fungal preservative challenges at 2% dosage, while 1,2-caprylyl glycol (caprylyl glycol) also passed bacterial and fungal preservative challenges at 1.5%.

Octyl glycol possesses good preservative and antibacterial effects and can be used alone or in combination with other substances as an "additive-free preservative," thus replacing traditional preservatives. For example, a combination system of octyl glycol and 1,2-hexanediol can be used alone to prepare preservative-free products, with an effective preservative effect achieved at a mass fraction of 0.5% to 1.0%. Octyl glycol exhibits good synergistic preservative effects when combined with mild preservatives such as p-hydroxyacetophenone and potassium sorbate.

Octoyl glycol is an ortho-alkyl diol with good compatibility (possessing two hydroxyl groups, it is well miscible with many other chemicals), good antibacterial effects, and low irritation. It can be added as a preservative and humectant to "additive-free preservative" products. Its effectiveness is further enhanced when used in combination with other preservative alternatives, such as p-hydroxyacetophenone and 1,2-hexanediol.