Review of 4 Testing Methods to Support Microbiome Friendly Claims in Skincare Products

Human skin is not only a protective barrier but also an ecosystem inhabited by various microorganisms, known as the skin microbiome. The balance of this microbiome is essential for maintaining skin health and protecting against pathogens.

In the cosmetics and skincare industry, there is a growing trend of products with microbiome friendly claims, referring to formulations designed not to disrupt the balance of the skin’s microbiota. This is important because some products can cause dysbiosis, an imbalance of microorganisms that may trigger skin problems.

However, these claims still face challenges in terms of definition and standardization of testing. Evaluations generally include microbial quality, balance, diversity, and vitality.

Various methods such as microbial culture, co culture assays, 16S rRNA sequencing, and resazurin assays are used to scientifically support these claims.

• Methods for Testing Microbial Quality in Skincare Products
• Methods for Testing Microbial Balance in Skincare
• Methods for Testing Microbial Diversity in Skincare Products
• Methods for Testing Microbial Viability in Skincare Products

Methods for Testing Microbial Quality in Skincare Products

The quality of microorganisms in cosmetic products must be tested to ensure the absence of pathogenic contamination. One commonly used method is the Total Plate Count (TPC), a culture based technique used to quantify the number of viable microorganisms in a sample.

This method can be applied to various skincare products by growing microorganisms on specific media. Plate Count Agar (PCA) is used for bacteria, while Sabouraud Dextrose Agar (SDA) is used for fungi and yeast.

Although simple and widely used, TPC is highly dependent on testing conditions. Factors such as media quality, inoculation technique, as well as incubation temperature and time must be well controlled to ensure accurate results.

Methods for Testing Microbial Balance in Skincare

The balance of microorganisms on human skin plays an important role in maintaining skin health. However, the use of cosmetic products has the potential to disrupt this balance, making post use testing essential before a microbiome-friendly claim can be made.

This testing aims to determine whether a product affects the balance between beneficial bacteria and other microorganisms. One method that can be used is the co culture assay, a technique that simulates interactions between microbes within the same environment.

In this method, two types of microorganisms are grown together so they can interact directly. One commonly used approach is the cross streak method, in which the first microbe, such as a probiotic bacterium, is streaked onto an agar medium. Then, the second microbe, such as a pathogenic bacterium, is streaked across the first line.

Observations are then made to determine whether the growth of the second microbe is inhibited. If inhibition occurs, this indicates an antagonistic effect or the ability of the first microbe to suppress the growth of other microorganisms.

This method is highly relevant for cosmetic products containing beneficial bacteria, such as lactic acid bacteria. In addition to assessing viability, co culture assays also provide insight into microbial interactions, making them more representative in evaluating the balance of the skin microbiome.

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Methods for Testing Microbial Diversity in Skincare Products

Microbial diversity must be analyzed to ensure that cosmetic products do not reduce the variability of the skin microbiome. One commonly used method is microbial community profiling using 16S rRNA sequencing, which enables comprehensive analysis of bacterial composition. The 16S rRNA gene is present in all bacteria and contains both conserved and variable regions, making it suitable for identification. The process includes DNA extraction from skin samples before and after product use, followed by PCR amplification and sequencing using technologies such as Illumina MiSeq.

The sequencing results are then analyzed using bioinformatics by comparing them with reference databases to determine bacterial species. This method helps identify changes in both the composition and abundance of bacteria after product use.

Methods for Testing Microbial Viability in Skincare Products

Evaluating the effects of cosmetic products on the microbiome is also necessary to determine whether the product kills beneficial microbes or maintains their viability. One method used is the resazurin assay, which measures bacterial viability and metabolic activity.

This method involves adding the cosmetic product to a culture of skin bacteria, followed by the addition of resazurin. This compound is initially blue but turns pink (resorufin) when reduced by living cells.

This color change serves as an indicator that the microorganisms are still metabolically active. If the pink color remains observable, it indicates that the microbes are still alive, suggesting that the product does not disrupt the balance of the skin microbiome.

Amid the growing trend of microbiome based skincare, scientific validation is key to differentiating your product in the market. Claims without data can pose risks to your brand reputation. Conduct appropriate testing methods with IML Testing and Research to ensure every claim is backed by strong and reliable evidence.

Author: Dherika
Editor: Alphi

References

Hossain T. J. (2024). Methods for screening and evaluation of antimicrobial activity: A review of protocols, advantages, and limitations. European journal of microbiology & immunology, 14(2), 97–115.

MyMicrobiome. (n.d). Microbiome-friendly Certification Cosmetics.

Oliva, A., Miele, M. C., Al Ismail, D., Di Timoteo, F., De Angelis, M., Rosa, L., Cutone, A., Venditti, M., Mascellino, M. T., Valenti, P., & Mastroianni, C. M. (2021). Challenges in the Microbiological Diagnosis of Implant-Associated Infections: A Summary of the Current Knowledge. Frontiers in microbiology, 12, 750460.

Yakobi,S.H., & Nwodo, U.U. (2025). Microbiological methodologies: Comparative evaluation of microbial community and enhanced antibiotic susceptibility testing. Electron Journal of Biotechnology, 74.