DSM exploratory research:

UV and the skin microbiome

The skin microbiome has been gaining increasing attention within beauty and personal care due to its role in human health and wellbeing, and it may now also become a new frontier in sun care.

By forming a protective barrier on our skin, the microbiome provides a first line of defence against external stressors, including UV radiation [1]. However, sun care and the use of UV filters is one area of personal care where more work is required to understand the relationship with the skin microbiome.

At DSM, we recognized this need and conducted the first clinical study exploring the benefits of UV filters for the skin microbiome upon UV exposure. As well as confirming an impact of UV radiation on microbial composition, our photoprotection expert team is the first to show an active benefit of sunscreen application for the skin microbiome and its protective function. Within this, we identified Lactobacillus crispatus as a key player within the UV-irradiated skin microbiome – a novel and exciting finding for the skin microbiome field.

We also explored the associated benefits for consumers, where UV filters that support L. crispatus populations can help preserve and strengthen the skin’s natural resilience after UV exposure.

For sun care developers, these insights feed into the identification of UV-protective ingredients that can be used for skin resilience-strengthening formulations – including a selection of microbiome-friendly-certified PARSOL® UV filters.

Here we explore this topic in more detail, including the outputs of our study and key takeaways for UV-protective personal care developers.

What is the skin microbiome and how is it affected by UV radiation?

The skin microbiome is a diverse community of microorganisms, including bacteria, fungi, and viruses, that reside on human skin (Fig. 1) [2].

These microorganisms and their interactions with the environment play a crucial role in supporting our skin health and overall wellbeing – for example, by shielding our skin from potential pathogens to support our protective skin barrier and immune system [3].

As our understanding of this complex ecosystem has grown, we have also seen how protecting the skin microbiome can support healthier skin. Maintaining a balanced, healthy microbiome is vital for these dynamics, with both quantity and quality being important. The skin microbiome adapts to internal and external factors, such as age, lifestyle, and environment. As the microbiome resides at the boundary between an individual and the environment, the skin microbiome is clearly influenced by environmental factors [4].

When it comes to UV radiation and the skin microbiome, only little evidence exists. For example, it was shown that erythema doses of UV irradiation had an impact on bacterial composition of subjects [5] and that cellular and immune response to UV were dependent on an intact skin microbiome [6]. Several UV filters have also been tested in the industry and proved to have no detrimental effect on the skin microbiome, but no studies have fully explored this relationship, or considered whether there could be any active benefit by UV filters for the skin microbiome.

Recognizing a need to better investigate the impact of UV exposure on the skin microbiome and any potential advantages of UV filters, we designed and executed a pioneering exploratory clinical study to explore these relationships.

Fig. 1 | The skin microbiome. The diverse community of microorganisms that live on the surface of our skin – including bacteria, fungi. Bacteria are the most abundant microorganisms on the skin. Bacterial composition will differ depending on factors such as body site by moist, dry, or oily skin conditions. Illustration adapted from Byrd et al [2].

DSM’s pilot trial for UV and the skin microbiome

The two key objectives in the clinical pilot study were:

1. To evaluate the impact of erythemal UV exposure on the skin microbiome
2. To determine if sunscreen offers a protective effect for UV-exposed skin microbiome

We chose a study design with 10 female volunteers, each providing skin samples from four skin zones on their upper middle back, i.e., untreated/unexposed, untreated/exposed, placebo and SPF20 treated on exposed skin. The time points just before and 2 hours after erythemal UV exposure (2 Minimal Erythema Doses) were considered. Skin swabbing samples were analyzed for changes in skin microbiome composition.

(i) Skin microbiome diversity change
Analysis from sequencing of the skin samples showed that both UV irradiation and treatment had a distinct impact on the relative abundances and diversity of the different bacteria found within the skin microbiome (Fig. 2).

Fig. 2 | Distinct changes in the global diversity within the skin microbiome upon UV irradiation and treatment. Relative abundances and diversity of bacterial composition of subject V1 by conditions

(ii) Protection of Lactobacillus crispatus
Within the highly diverse skin microbiome community, we identified the bacterial species Lactobacillus crispatus that was readily reduced after UV exposure and on the same time protected by the sunscreen treatment

Lactobacilli are a group of lactic-acid-producing bacteria that are recognized as a key component of the innate immune response and are known to be beneficial for human health [7]. Lactobacilli are key to maintaining a stable and acidic environment, and through this help to preserve skin barrier function and resilience. Lactobacilli also help to maintain the overall balance of the microbial community and protect against skin pathogens and infections.

L. crispatus is one type of Lactobacillus bacteria that has previously been identified as a key member of the vaginal and intestinal microbiomes [8, 9], yet little is known around its dynamics on the skin [10, 11]. L. crispatus was found to be the most abundant Lactobacillus species on the skin in our study and we are among the first to identify the potential of L. crispatus as a relevant member for the natural skin microbiome. We have seen that the relative abundance of L. crispatus changed significantly within the UV-irradiated skin microbiome (Fig. 3). We found that UV exposure decreased the abundance of L. crispatus in vivo, confirming that UV radiation can indeed cause imbalances in the skin microbiome with potential implications for skin health. In addition, an active benefit of UV protection was seen in vivo, with the SPF 20 sunscreen preventing the UV-induced reduction of L. crispatus.

Fig. 3 | Relative abundance of L. crispatus after irradiation and treatment. Using sequencing analysis, we observed changes in the relative abundance of L. crispatus between control, UV-irradiated and sunscreen-treated samples.

Following the observation that specific microorganisms such as L. crispatus can benefit from UV protection, we conducted further in vitro experiments that confirmed our findings. Additionally, we could identify an active benefit of selective UV filters on beneficial bacteria:

PARSOL® 340, PARSOL® ZX, PARSOL® 1789 and PARSOL® EHT effectively protected L. crispatus abundance upon UV radiation.

We also identified that a smart PARSOL® filter combination with e.g., our microbiome-friendly certified* UV filters PARSOL®1789, PARSOL® Shield, and PARSOL® EHT, allows SPF to be maximized while protection of symbiotic bacterial species is maintained to strengthen UV-exposed skin resilience.

In addition, we have seen in vitro that the UV filters used within the test showed selective protective behaviour: populations of L. crispatus or Staphylococcus epidermidis, which was considered as another beneficial reference species, were supported by UV filters; in contrast, we observed that growth of Cutibacterium acnes could be attenuated by certain UV filters.

C. acnes is a major component of the skin microbiome, but it has been widely linked to the development of inflammatory acne in the event of a skin microbiome imbalance and under use of comedogenic ingredients [12-14]. We could see that C. acnes population could be reduced by selected UV filters – such as PARSOL® 1789, PARSOL® EHS and PARSOL® 340 – while also maintaining balance by supporting populations of other bacteria such as S. epidermidis.

These findings suggest the specific use of those filters for sunscreen formulations that are tailor-made for acne-prone skin.

What do these results mean for consumers and sun care developers?

(i) Empowering natural skin resilience
At DSM, we have observed a growing consumer preference for products that support and enhance the natural properties of the skin. Our study addresses this consumer need by highlighting a clear benefit for the skin.

We have shown that a selection of UV filters not only shield against harmful UV radiation, but also enhance the skin's natural resilience by protecting the survival of beneficial bacteria within the skin microbiome. Using sun care products containing an appropriate filter combination can therefore support skin health. It helps to maintain skin structure and function by preserving the skin microbiome natural function. This increased resilience can also help protect against the damaging consequences of environmental stressors such as UV radiation, and delay and counteract the effects of skin aging [15].

(ii) UV filter selection and formulation for sun care developers
As well as entering new area of research, the study results were translated into two patent applications. Our insights help sun care developers to create formulations with additional differentiating potential in the market, driven by their choice of selected PARSOL® UV filters.

Through our work, we also provide recommendations of which UV filters are best suited for skin health benefits (Fig. 4) and support a healthy skin microbiome.

Fig. 4 | Recommended UV filters and combinations to support Lactobacillus crispatus and control C. acnes

If choosing to use these filters in a sun care formulation, we additionally provide formulators tools to promote skin microbiome benefits in the final product – including formulation guidance to support the formulation of microbiome-friendly products based on our established experience in this area.

For example, to support the achievement of a microbiome-friendly claim, formulators can use certified microbiome-friendly* filters from the DSM PARSOL® portfolio, such as PARSOL® 1789, PARSOL® Shield and PARSOL® EHT. We also offer Flor’Active Defense SPF 30 – a first-to-market certified microbiome-friendly* sunscreen formulation proven to respect the skin’s microbial diversity, protect against UV irradiation and support skin health (Fig. 5).


Fig. 5 | Flor’Active Defense SPF 30 – a first-to-market certified microbiome-friendly sunscreen formulation.

For more information on the study or for UV filter and formulation support, please get in touch with us.

For more information on the skin microbiome, please visit our Secret Life of Skin content hub.

Published on 27 April 2023


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