513 Evolution and Challenges of Sustainability
acetylsalicylate, acetaminophen, sodium benzoate, and cinnamate induced expression of
the marRAB operon of E. coli.169 This is important because the marRAB operon responds to
several compounds including tetracycline and chloramphenicol.172 McDonnell and Russell
indicated that plasmid-mediated efflux pumps were responsible for resistance to many
antibiotics and biocides.173
The American Society for Microbiology has classified AMR to be a top priority.174 In 2023,
Darby et al. indicated that antibiotic resistance is a global health emergency, and resistance
has been detected to all antibiotics currently in clinical use.175 Products should not contain
ingredients that cause AMR. Products with such ingredients may cause AMR when released
into the environment (i.e., when washed off the skin during bathing), and application of
such products onto skin may cause AMR in some members of the skin microbiome—
neither of these outcomes is sustainable. Although over-prescription of antibiotics and use
of antibiotics in agriculture and raising farm animals is known, the cosmetic industry
may unwittingly be contributing to the problem of AMR. Orth stated that cosmetic and
drug manufacturers should have programs to ensure that their products will not encourage
the development of drug-resistant microorganisms.176 It is recommended that cosmetic
manufacturers address this issue. This will require additional risk assessment and testing,
but it will help identify ingredients that cause AMR so that they can be eliminated—this
is needed for products to be sustainable.
SUSTAINABLE PRODUCTS THAT WORK WITH THE SKIN MICROBIOME
Sustainability can be achieved through activities that do not have adverse effects on
the environment or cause loss of biodiversity, which is necessary for living populations
to survive stressful changes in their environment. The cosmetic and drug industries are
beginning to address sustainability by using ingredients from renewable resources and
by replacing packaging materials that are not biodegradable (e.g., plastic) with alternative
materials. Ingredients, including preservatives and multifunctional ingredients, may be
sourced from companies committed to address sustainability, and products made with
such ingredients may have negligible carbon footprints or minimal effects on biodiversity
however, there may be issues related to the effect of preservatives and multifunctional
ingredients in products on the skin/skin microbiome ecosystem.
Spragge et al. observed that diversity involving “key species” contributed to colonization
resistance to prevent pathogen infection in the GI tract.161 It is believed that a similar
situation may occur on skin, so it is important that preservatives, multifunctional
ingredients that have antimicrobial action, and other ingredients, do not adversely affect
skin microbiome diversity. Although it has been estimated that Cutibacterium, Staphylococcus,
and Corynebacterium genera constitute up to 80% of the entire skin microbiome,73 we do
not know if bacteria in these genera or the Malassezia spp. on the scalp and upper body
constitute the key species necessary for survival and maintenance of homeostasis when
the microenvironment of skin is changed following changes in the environment or use
of cosmetic products. It is recommended that studies be conducted to determine the key
species in various skin sites of healthy individuals so that these microorganisms may then be
used as biomarkers to assess the effect of product use on the skin microbiome in these sites.
Products that have no adverse effects on these biomarkers or the healthy skin microbiome
are sustainable because they will help prevent dysbiosis and maintain homeostasis.

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