514 JOURNAL OF COSMETIC SCIENCE
SIGNIFICANCE OF UNCULTURABLE MICROORGANISMS AND VIRUSES ON SKIN
It has been estimated that about 80% of the skin microbiome species are culturable.72 Newer
approaches to identifying microorganisms include molecular methods (e.g., 16S rRNA
sequencing), which enable detection of microorganisms that are present in low numbers
or that are unable to grow on traditional culture media (e.g., archaea and bacteria that are
viable but nonculturable).106,177 We do not know the significance of these microorganisms.
Studies are needed to determine if these microorganisms are viable, whether they are
commensals or transients, and if they influence the skin microbiome.
Lytic phages prevent overgrowth of harmful bacteria by causing lysis, whereas temperate
phages are thought to promote survival of commensal bacteria in the GI tract by providing
genes that allow these bacteria to grow.178 The balance of lytic and temperate phages on
the bacterial population is necessary for a healthy GI microbiome. Viruses (phages) are
part of the skin microbiome. It is believed that a similar balance occurs on skin and that
deviations from a balanced microbiome (i.e., dysbiosis) may be associated with inflammatory
dermatological conditions including acne, AD, and psoriasis.179 Phage therapy involves
the use of phages that selectively target objectionable bacteria in order to alleviate the
associated health conditions. Phage-based therapeutic strategies have shown promise for
the treatment of a variety of dermatological conditions,75 and larger scale confirmatory
studies should be conducted to validate phage therapy for treatment of skin disorders.
CONCLUSION
There has been an evolution of cosmetic preservation over the past 75 years. The cosmetic
industry became aware that a substantial percentage of products were contaminated with
microorganisms, and this problem was largely addressed by more rigorous preservative
efficacy testing to improve product preservation, reformulation of products, and better
compliance with GMPs. Rapid, miniaturized, labor-saving methods of preservative efficacy
testing using stricter acceptance criteria have been developed that enable testing to be
completed in two weeks or less. Innovative new methods require less culture media and
disposable items (e.g., pipettes and Petri dishes), which results in less waste, so they are more
environmentally friendly than compendial or trade association methods. Sustainability will
be improved by validation and adoption of newer methods of preservative efficacy testing
that have less environmental impact.
Sustainability concerns have provided the basis for further evolution of cosmetic preservation.
Preservatives are biocides that may have adverse effects in the environment and possibly on
the skin microbiome, and ingredient suppliers are working with manufacturers to contend
with this issue by providing preservatives and multifunctional ingredients from natural
sources that are sustainable. Preservatives may cross-react with antibiotics to cause AMR,
which is a very serious global health concern. This issue needs to be addressed to prevent
increases in drug resistant microorganisms due to cosmetic products.
Concern over carcinogenicity due to formaldehyde and formaldehyde donors resulted in
transitioning away from the use of preservatives to the use of multifunctional ingredients
with antimicrobial action to reduce or replace these preservatives. The cosmetic industry
doubled down on replacement of parabens with multifunctional ingredients following a
report indicating that there may be a possible link between parabens and cancer. This

515 Evolution and Challenges of Sustainability
evolution has involved the use of hurdle technology that enables cosmetic scientists to
formulate products with reduced levels of preservatives or products that are preservative-free.
The evolution of cosmetic preservation is expanding from merely being focused on
preservative systems that prevent product contamination to products that preserve the
healthy skin microbiome. We are beginning to determine the composition of the skin
microbiome, the benefits of microbial diversity in sustaining the microbiome, and the
crosstalk between the microorganisms and the skin that benefits skin physiology and
helps maintain homeostasis. Sustainable cosmetic products should work with the skin
microbiome to maintain microbial diversity and to prevent dysbiosis that may result in
skin disorders. It may be possible to use selected microorganisms as probiotics, to use
phages to prevent growth of undesirable microorganisms, or to use compounds identified
as prebiotics to stimulate growth of desirable skin microflora to maintain homeostasis. The
evolution of cosmetic preservation will continue as we learn more about environmentally
friendly preservative-free products that are sustainable because they benefit the healthy
skin/skin microbiome ecosystem as they beautify and promote attractiveness of the skin.
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