Cosmetic preservatives and the microbiome: What is the impact?

While research into the microbiome of the epidermis - the millions of microorganisms that exist on our skin - has been developing significantly over the last decade, there is still much to be learnt about how this highly diverse micro-environment can impact the health and appearance of our body’s largest organ.

While an optimal balance between good and bad bacteria, along with a healthy diversity is now known to be essential, exactly how functional and supportive ingredients can impact this is still being investigated. Read more on how to formulate with pre- and probiotics, and how they support skin health, in this blog. 

This article will look at the existing knowledge around how preservative use in cosmetic formulas may impact the microbiome, with tips on how to make the right choices for your next cosmetic formulation developments to ensure you are creating ‘microbiome friendly’ formulas.

Choosing the correct preservative for a cosmetic formula to ensure it is safe, stable and effective over its shelf life is a crucial quality control aspect.

However, more recently, with studies into how important a balanced microbiome is for optimum skin health, the discussion of which preservatives, and how much should be used, has diverged from just considering the needs of the formula to include the impact they have on the skin.

As an over-arching principle, discussions have centered around the need for an adequately preserved cosmetic product to ensure consumer safety by avoiding the presence of known harmful bacteria - that is, keep the product safe for consumer use over its shelf life.

Additional criteria have focused on ensuring the safety of a preservative (or blends of various preservatives) when used within regulatory limits, including the cumulative use of multiple types of personal care products within any 24-hour, 7 day and in some cases, monthly period. In other words, ensuring exposure to multiple and various preservatives are still safe for consumer application. Watch this video to better understand the use of preservatives and regulatory limits in cosmetic formulas.

The regulatory limits for all preservatives have used these concepts to guide limits of use in both wash-off and leave on personal care products by measuring issues of irritation, redness and associated symptoms, as well as more in-depth physiological and toxicological studies from various sources.

While this approach means we can use preservatives within their recommended limits in a safety-oriented way with minimal visual or sensory impact on a consumer, it has not considered what is happening at the microbiome level.

Many authorities still consider that if there are no debilitating or harmful effects on the skin, there is unlikely to be any detrimental effect on the skin microbiome either. However, recent research suggests it may not be as simple as that. 

In 2021, a study was conducted into the use of eleven different preservative combinations to see if and how the impacted 3 key microbiome populations. Results showed the most beneficial combinations of ingredients were actually only preservative boosters, and therefore not sufficient for effective cosmetic formula preservation on their own.

It also showed that a few commonly used broad spectrum preservatives did not impact a healthy population of essential microbiota; however it did not consider many other commonly used cosmetic preservatives, nor did it consider more than these most common skin microbiota.

A study in late 2024² has proven that cosmetic preservatives in personal care do impact skin quality parameters. They used microbiome profile-based subgrouping to show that preservative-free products displayed reduced skin folds, fine lines and redness - a clear link to physical signs of ageing and skin health.

While the overall microbiome diversity did not show a significant difference amongst products used, the preliminary findings from this small-group study highlighted the importance of further research in this area to better identify how different skincare products can impact the skin microbiome, along with the preservatives they contain. Visit this page to learn about preservative-free cosmetic formulation tips.

Another study³ into how the skin microbiome can impact skin ageing showed a positive correlation between reduced skin barrier function and decreased microbial diversity.

While this study did not specifically examine the impact of specific preservatives on the microbiome, it does show that either changes to the skin barrier, or microbiome that impact the skin barrier, will impact the overall health of the skin. 

Functional ingredients such as lipids, emulsifiers and surfactants, and supportive ingredients such as preservatives can all have a significant impact on skin barrier health and the microbiome.

More controlled research using larger groups of consumers is needed to definitively measure exactly how different preservatives (and combinations of ingredients) may impact a healthy microbiome.

Preservative free skincare, where possible, safe and suitable, may be an effective way to maintain a healthy microbiome and reduce at the very least, micro-signs of skin ageing.

To make microbiome-friendly claims, cosmetic formulas should:

• contain cosmetic ingredients with proven efficacy to support microbiome health, and
• ensure regulatory compliant use of cosmetic preservatives that were specifically shown to be beneficial to the skins’ microbiome, and/or
• have efficacy data to show the final cosmetic formula has specifically been tested and proven to support the health of the microbiome.

Speak with your cosmetics suppliers and visit the Innovation Zone at your nearest in-cosmetics exhibition to seek out more microbiome friendly cosmetic ingredients. 

Happy formulating! 

References

1. Pinto, D., Ciardiello, T., Franzoni, M. et al. Effect of commonly used cosmetic preservatives on skin resident microflora dynamics. Sci Rep 11, 8695 (2021). https://doi.org/10.1038/s41598-021-88072-3
2. Wagner N, Valeriano VD, Diou-Hirtz S, Björninen E, Åkerström U, Engstrand L, Schuppe-Koistinen I, Gillbro JM. Microbial Dynamics: Assessing Skincare Regimens' Impact on the Facial Skin Microbiome and Skin Health Parameters. Microorganisms. 2024 Dec 21;12(12):2655. doi: 10.3390/microorganisms12122655. PMID: 39770857; PMCID: PMC11728252.
3. Mahjabin Ferdaous Mim, Mahmudul Hasan Sikder, Md. Zahid Hasan Chowdhury, Ashkar-Ul-Alam Bhuiyan, Nayeematul Zinan, Shah Mohammad Naimul Islam, The dynamic relationship between skin microbiomes and personal care products: A comprehensive review. Heliyon, Volume 10, Issue 14, 2024, e34549, ISSN 2405-8440, https://doi.org/10.1016/j.heliyon.2024.e34549.

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