Preservatives are one of the most common chemical materials in daily life. They are used widely in various commercial products, such as foods, house hold products, cosmetics, and even medicines. Most preservatives are known to people as dangerous materials. To reduce potential risk of them, many researchers have tried to minimize the total amount of preservatives or to replace them with safer ones in their formulations. Natural compounds, like plant derived essential oils and extracts can be used for the preservation of household products and cosmetics. However, they are not used widely, because they have strong odor and weak antimicrobial effects compared to commonly used preservatives.
1,2-Alkanediols such as 1,2-hexanediol (C6), 1,2-octanediol (C8), 1,2-decanediol (C10) are now frequently used in cosmetic applications because of their excellent moisturizing properties, high water solubility and effectiveness as a solvent. Additionally, these aliphatic 1,2-diols possess anti-microbial activity. Several studies have addressed the effectiveness and usefulness of 1,2-alkanediols with varying alkane chain length in controlling microorganisms. Minimum inhibitory concentration (MIC) was determined for a number of 1,2-alkanediols. MIC results showed that the anti-microbial activity of 1,2-alkanediols increases as their alkane chain length increases.
Skin contributes to the first line of defence against any foreign materials outside of our body as a physical barrier. Skin disruption for any reasons ends up inflammatory skin diseases. As an immune sentinel, keratinocytes can recognize foreign or dangerous stimuli from outside and release a series of cytokines. In response to these stimuli, preformed cytokine interleukin-1α (IL-1α) is released from the keratinocytes as the first step in the inflammatory cascade. IL-1α stimulates other keratinocytes and fibroblasts to produce and release more IL-1α and other primary pro-inflammatory cytokines, IL-1β, IL-6,IL-8 and tumour necrosis factor-α(TNF-α). It is very important to identify the risk of 1,2-alkanediols as a cosmetics preservative, so we tested the three kinds of experiments: cytotoxicity test, quantitative sandwich enzyme immunoassay and h-CLAT.

It was found that cytotoxicity of 1,2-alkanediols increases as their alkane chain length increases as same at antimicrobial test. The values of cytotoxicity(IC50) ranges between 0.006 and 0.284%.
In quantitative sandwich enzyme immunoassay study, it was found enhanced level of IL-1α as their chain length decreased. The level of vascular endothelial growth factor (VEGF) also increased more than level of baseline (not treated).
In h-CLAT assay, it was found that 1,2-decanediol, which has the strongest cytotoxicity, showed the weakest skin sensitization potential. These results were derived from the difference between the methods. This method, h-CLAT, is not an animal test such as GPMT (Guinea Pig Maximization Test) or LLNA (Local Lymph Node Assay), but a biological experiment using THP-1 cell for identifying the skin sensitization potential. After the announcement of EU (2013) about the ban of animal tests in cosmetics, cosmetic companies only use ingredients that have not performed any kind of animal tests for the purpose of cosmetic applications. The limitations of treated sample concentration and preference of vehicle leaded to these results.
Based on the results from above, we have determined the concentrations for cosmetic preservatives and made three kinds of sample formulations: toner, emulsion and cream. We have also performed the preservative efficacy test to identify the activities as a preservative and performed a human patch test and repeated open application test (ROAT) to examine the skin irritation and sensitization potentials. The selection and recruitment of subjects of the human tests were carried out in accordance with the ethical principles set out in the Declaration of Helsinki and International Ethical Guidelines for Biomedical Research Involving Human Subjects after approving in laboratory’s institutional review board.

The tested samples, which include three kinds of 1,2-alkanediols, had an excellent potential as preservatives and weak damaging impacts, such as irritation or sensitization , on human skin.

The results suggest that there are some predictable relationships between skin irritation, sensitization potentials, anti-microbial activity and the chain length of 1,2-alkanediol, but these relationships may be complex. The skin irritation, sensitization potentials and anti-microbial activity of 1,2-alkanediols can also be influenced by varying the formulations of cosmetic products.