Ultraviolet radiation (UVR) is a known environmental key factor for premature skin aging. The skin microbiome’s role in human health & wellbeing is becoming better understood within the personal care and beauty industry. However, the impact of UVR on the skin microbiome is poorly understood and investigated.
Dsm-firmenich’s designed and executed a pilot clinical study to explore these relationships to evaluate the impact of erythemal UVR exposure on the skin microbiome and to determine the protective effect of an SPF 20 sunscreen versus placebo on the UV-exposed microbiome.
Data obtained were recently published in the International Journal of Cosmetic Science.
Ten pre-menopausal female volunteers were recruited and treated with an SPF 20 sunscreen and placebo formulation (without UV filters) on their upper middle backs and irradiated with an erythemal dose (2 MED) by a solar simulator. Skin swabbing samples from four zones (i.e., unexposed, exposed, sunscreen- and placebo-treated on exposed skin) were collected for the microbiome analysis before and 2 hours after UV exposure, respectively, and processed via shallow 16S rRNA sequencing. Apart from significant inter-individual differences, both, UV irradiation and treatment, had a distinct impact on the relative abundances and diversity of the different bacteria found within the skin microbiome. Indeed, alpha diversity was impacted by significant inter-individual differences and by treatment rather than by irradiation. Cutibacterium acnes was found to be most abundant and a confounding factor for diversity. On a species level Lactobacillus crispatus, a component of the innate immune system, was negatively associated with UVR and placebo treatment, whereas there was a positive association with the sunscreen treatment. The sunscreen treatment also favored an interaction network with central Micrococcus genus. Authors suggested that UV filters preserve the functionality of such key players and ultimately, may help to preserve skin barrier function and resilience upon UV stress.
In the second part of the study, researchers developed an in vitro UV method using single UV filters and combinations thereof applied to the bacteria before UV irradiation. The experimental results showed that both single UV filters and combinations had specific effects on the survival rates of L. crispatus, C. acnes, and S. epidermidis.
Overall, the study demonstrated that UVR protection can be expanded to the microbiome and identified potential microorganisms and bacterial interactions that were associated with an SPF 20 sunscreen treatment. Using microbiome-friendly sun care products containing optimized filter combinations can therefore support skin health maintaining skin structure and function and preserving a natural skin microbiome. The specific protection of L. crispatus as a key player in the UV-exposed skin microbiome and reduction of C. acnes population by UV filters might lead to new cosmetic concepts for photoprotection.