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Understanding preservatives
Preservatives are added to cosmetic products to protect against the growth of pathogenic microorganisms and to extend the product's shelf life. However, as preservatives remain active on the skin upon application, there is a risk that they may alter the skin microbiome.
A summary of what we know:
The predominant genera of bacterial species on the skin’s microbiome are Cutibacterium, Staphylococcus and Corynebacterium (Wang et al., 2018)
In particular, C. acnes, S. epidermidis, and S. aureus act usually as commensal bacteria since they are harmless when the skin is healthy and are in a mutualistic relationship with the cutaneous system (Fournière et al., 2020; Pinto et al., 2021)
Among these species, S.epidermidis is the most beneficial as it has been shown to protect against inflammation, infections, and cancer through interactions with keratinocytes, T cells, and other constituents of the skin microbiome (Stacy and Belkaid, 2019; Zhang et al., 2023)
An in vitro study testing eleven different combinations of preservatives found that those containing hydroxyacetophenone, phenylpropanol, propanediol, caprylyl glycol, tocopherol, and tetrasodium glutamate diacetate were most suitable for restoring dysbiosis as they act moderately inhibiting C. acnes and strongly S. aureus without simultaneously inhibiting the growth of S. epidermidis (Pinto et al., 2021)
An in vivo study on the leg skin microbiome revealed that different preservation systems had a minimal impact, suggesting that preservative systems do not have any detrimental impact on the structure or diversity of the skin microbiome for both rinse off and leave on products (Murphy et al., 2021)
Industry impact & potential:
Symrise Cosmetic Ingredients multifunctional ingredients SymSave H and SymDiol 68 have shown to act in combination as a product protection system that maintains the natural flora of the skin
More in vivo studies are needed to measure the long-term, accumulative effects of preservatives on the skin’s microbiome
Our approach:
We believe that cosmetic companies should re-evaluate their use of preservatives to help consumers maintain a healthy microbiome. Through formulation support and invivo testing we can advise on the most suitable preservative choice for your formulation and substantiate microbiome-related claims.
References:
Fournière M, Latire T, Souak D, Feuilloley MGJ, Bedoux G. Staphylococcus epidermidis and Cutibacterium acnes: Two Major Sentinels of Skin Microbiota and the Influence of Cosmetics. Microorganisms. 2020; 8(11):1752. https://doi.org/10.3390/microorganisms8111752
Murphy B, Hoptroff M, Arnold D, Eccles R, Campbell-Lee S. In-vivo impact of common cosmetic preservative systems in full formulation on the skin microbiome. PLoS One. 2021 Jul 7;16(7):e0254172. doi: 10.1371/journal.pone.0254172. PMID: 34234383; PMCID: PMC8263265.
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
Stacy A, Belkaid Y. Microbial guardians of skin health. Science. 2019 Jan 18;363(6424):227-228. doi: 10.1126/science.aat4326. PMID: 30655428.
Wang, Wen-Ming; Jin, Hong-Zhong. Skin Microbiome: An Actor in the Pathogenesis of Psoriasis. Chinese Medical Journal 131(1):p 95-98, January 05, 2018. | DOI: 10.4103/0366-6999.221269
Zhang W, Wang X, Zhao L, Gu Y, Chen Y, Liu N, An L, Lu Y, Cui S. Effect of leave-on cosmetic antimicrobial preservatives on healthy skin resident Staphylococcus epidermidis. J Cosmet Dermatol. 2023 Jul;22(7):2115-2121. doi: 10.1111/jocd.15690. Epub 2023 Mar 9. PMID: 36895166.
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