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The skin microbiome consists of billions of microorganisms. Many microbiota are specialized under certain environmental conditions and in different body regions.1 The composition of the microbiome is dependent upon temperature, moisture, nutrients and pH, and other physical and chemical parameters. Every human being has an individual microbiome that is temporally stable but unlike a fingerprint or DNA code, it can change over time.1-3
As there are beneficial interactions between both the various specimens within the microbial community and the microbial community and the host immune system, good skin diversity is desirable.1 In addition, diverse communities adapt better to environmental changes in general.
In fact, a low diversity can be found in unhealthy skin and diseases such as atopic dermatitis,1 where certain species dominate the skin flora and are correlated with typical clinical symptoms. Due to these symptoms, cosmetic scientists seek ways to maintain or even improve the diversity of the microbiome.
To analyze the influence of substances or external factors on the skin microbiome, the individuality of the microbiomes must be considered. Therefore, two diversity indicators are important when addressing this question: alpha and beta.
The alpha diversity is a measure of the effective number of species and therefore the microbial richness in a particular environment, localization, sample or sample group. It is a measure of how evenly the different microbes are distributed in a sample. To calculate this, the Shannon or Shannon-Wiener Index can be utilized. This statistical tool is a relative measurement that essentially provides an uncertainty value; thus, the higher the uncertainty, the higher the index and the greater diversity—and the better the skin condition.
The beta diversity is a measure of the difference between microbial communities from different environments, localizations or samples. This enables the comparison between groups or areas that have been treated differently. Both alpha and beta indicators are important when assessing the impact of substances or measures on the microbiome.
As is well-known, preservatives are designed to inhibit the growth of microorganisms to protect products such as cosmetics from deterioration and users from unwanted infections by pathogens. However, it could be assumed that these active ingredients may also influence skin microorganisms. The present exploratory study sought to determine if this is the case by assessing the effect of one preserved cosmetic product on the skin microbiome in comparison with an untreated control area over an extended 22-day period and under realistic use conditions.
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- Grice, E.A., et al. (2009). Topographical and temporal diversity of the human skin microbiome. Science 324(5931) 1190-1192. doi:10.1126/science.1171700
- Kim, H.J., et al. (2019). Segregation of age-related skin microbiome characteristics by functionality. Sci Rep 9 16748 https://doi.org/10.1038/s41598-019-53266-3
- Oh, J., Byrd, A.L. and Park, M. (2016). Temporal stability of the human skin microbiome. Cell 165(4) 854-866. doi:10.1016/j.cell.2016.04.008