535 Foreword
microorganisms. As the research marches forward, Garlet details the exciting correlations
that have been identified between the signs of aging and fluctuations in specific populations
of microbes on the skin.
Schaefer et al. conclude this special skin microbiome issue with an elegant in-depth
elaboration of the current state of knowledge involving the interconnectivity of the gut
and the skin microbiomes. The so-called “gut-skin axis” has been described in some depth
elsewhere and more rarely the reverse “skin-gut axis” has been speculated upon. Here,
the authors comment on the bi-directionality of this important axis of communication
between members of the human microbiome. They also highlight how metagenomic
sequencing technology has been a major paradigm change from the early days where our
understanding of the skin microbiome was limited to what could be cultured from the
skin, and how these new research efforts are rapidly expanding our understanding of these
complex interactions and how they provide greater resolution of the microbes that are part
of these pathways.
Collectively, these articles contribute to the substantive advancement in our understanding
of not just the components of the skin microbiome, but the intricate interconnectedness of
this diverse community and its impacts on skin health.
Many unanswered questions and nebulous aspects remain, assuring exciting future
revelations to be made in this area of research. This frontier of skin microbiome topics
includes the unheralded members of the skin microbiota that are less often mentioned:
the fungi, protists, archaea, viruses, and others yet to be fully characterized. Indeed, the
discovery of a new group of acellular biological entities composed entirely of RNA called
“obelisks” was reported in early 2024, and they appear to be associated with the gut and
oral microbiomes, which potentially could extend to the skin. Also, pathogenic varieties
of prions, another acellular biological entity, have been found to be “seeded” into human
skin under certain conditions. The archaea certainly present an intriguing mystery given
that they are representative of the third cellular domain of life on Earth and are frequently
characterized as environmental extremophiles. Their precise role in skin health has yet to
be defined, but there appears to be an age component as they are detected at their highest
levels at early ages up to adolescence when there is a pronounced drop in their abundance
only to resurge again around the age of 60. Similarly, metagenomic sequencing efforts
have shown the viral component of the skin microbiota seems to be dominated by DNA-
based viruses, which could have deeper meaning or be an artifact of genomic sequencing
techniques that favor DNA genomes. These are just a few of the tantalizing questions yet to
be answered, which will certainly provoke discussions of how and whether the personal care
industry can capitalize on the resulting findings to design, develop, and launch new classes
of active ingredients that can improve skin health by modulating these microbial targets.
As we celebrate the 75th anniversary of the Journal of Cosmetic Science, it is our sincerest hope
that you will appreciate these intriguing reports relevant to the ongoing effort to expand
our knowledge and understanding of the skin microbiome. This is a subject area that
continues to demonstrate a profound relevance to the maintenance of healthy, youthful skin.

536
J. Cosmet. Sci., 75.6, 536–552 (November/December 2024)
*Address all correspondence to Paul Lawrence, paul.lawrence@biocogent.com
Reviving a More Than Century-Old Technology for Modern
Skincare
PAUL LAWRENCE, BRIANNA SCACCHI, KIMBERLY DEW AND JOSEPH CECCOLI
Biocogent, Stony Brook, New York, USA (P.L., B.S., K.D., J.C.)
Accepted for publication August 2, 2024. Presented at SCC76 and recipient of 2023 Hans Schaeffer Award.
Synopsis
Research into the skin microbiome continues to accelerate at an unrelenting pace with an expanded
understanding of how these microbial constituents contribute to skin health. The largest group of these microbes
is the bacterial component which includes both beneficial and potentially problematic microorganisms. Some
of these exhibit dual roles of commensalism and antagonism with regard to maintaining healthy skin, and
as such, skin microbiome modulation efforts should be balanced and precise. To that end, interest has been
rekindled in a technology that dates back more than a century, so-called “bacteriophage therapy.” This entails
using the natural predators of bacteria in the environment to diminish their population levels viruses (or
bacteriophages) that exclusively target bacteria in a species-specific and sometimes strain-specific manner.
Here, we present the results of an investigation into using a collection of bacteriophages to target and diminish
the levels of Cutibacterium acnes, a member of the skin microbiome that can contribute to the development
of acne vulgaris. The bacteriophage cocktail successfully diminished specifically C. acnes both in vitro and
in vivo with no adverse effects detected. As other topical microbiome modulatory ingredients exhibit more
nonspecific antimicrobial effects on the skin microbiota, this approach offers an attractive, highly targeted
alternative.
INTRODUCTION
Our understanding of the significant contribution of the skin microbiome to overall skin
health rapidly increases with each passing day. Currently, the skin microbiome is one of the
most discussed new areas of skin care research—how the various microbial inhabitants of
the skin (skin microbiota) contribute to the pathogenesis of many skin diseases and disorders.
Indeed, the skin supports a rich community of microorganisms that includes bacteria,
fungi, archaea, protists, and viruses.1 Many of these microbes are considered commensals
as their habitation of the skin prevents the encroachment of pathogenic microorganisms.
Two of the most abundant bacterial species are the Gram-positives: Cutibacterium acnes and
Staphylococcus epidermidis.2 The former has been established to contribute to the “acid mantle”
of the skin that keeps many harmful microbes from getting a foothold through the action
of lipases that it secretes.3 The latter species secretes an enzyme called sphingomyelinase
that promotes the production of ceramides that reinforce the skin barrier.4