COSMETICS & PERSONAL CARE
As the composition of a healthy skin microbiota varies between individuals and body parts , maintaining a balanced composition unique to an individual is key . We therefore sought to identify ingredients and develop formulations that do not disrupt the complex microbial communities found on healthy skin .
Present study
Due to the complexity of full microbiome studies , in a first step , many typical galenic ingredients ( e . g . emulsifiers ( n = 10 ), polymers ( n = 6 ), polyols and preservatives ( n = 10 )) were screened using minimal inhibitory concentration ( MIC ) tests . The effects of substances on the growth of two beneficial microorganisms , Staphylococcus epidermidis and Cutibacterium acnes , plus the commensal Corynebacterium minutissimum , were evaluated . Three emollients were subjected to full microbiome testing with 16S rDNAbased analyses on human volunteers . The results were used to identify the most suitable ingredients and to develop formulations . These were then tested on 20 human volunteers , twice daily over four weeks , using 16S rDNA sequencing techniques ( Figure 1 ). The ‘ must haves ’ of skin care products , namely moisturising effects ( assessed via corneometry ), effects on skin barrier function ( measured using trans-epidermal water loss ),
Figure 3 – Formulation chassis used in testing '
and consumer acceptance ( via questionnaires ) were also evaluated . Stability testing was conducted at -20 ° C , 4 ° C , 29 ° C , 40 ° C , 50 ° C for three months , except for testing at -20 ° C and 50 ° C , which were conducted for one month only . Challenge testing was conducted according to EN ISO 11930 . Additional formulations containing bioactives were also developed , and formulation and microbiological stability tested .
Results
MIC results varied substantially depending on the ingredient type and composition tested ( Figure 2 ). In particular , emulsifiers and preservatives had a negative effect on microbial growth .
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Figure 2 – Identified ‘ best of ’ ingredients ( no adverse effects on skin microbiota at the concentrations shown and based on screening results )
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