Using a sunscreen is highly recommended to protect oneself from the harmful effects of the sun on the skin. However, recent studies indicate the possibility of a disruption to the skin microbiota, these micro-organisms that colonise our skin, through the use of sunscreen. What's the situation?
Does sunscreen alter the skin microbiome?
Published on October 4, 2024, by Kahina, Scientific Editor — 4 min of reading
Themes:
How does sunscreen act on the skin microbiome?
Researchers have recently questioned how sunscreen can affect the skin's microbiome. Indeed, a study led by Christel LEFRANCOIS and her team has shown that exposure to commercial sunscreen formulations altered the skin microbiome of fish. The relative abundances of bacteria Bacteroidota, Actinobacteroidota and Proteobacteria were significantly altered. Furthermore, the proliferation of certain genera, such as Mycobacterium, Tenacibaculum and Nocardia, was observed in the skin microbiome. Thus, sunscreens could potentially disrupt the first biological barrier against bacteria.
Most tested sunscreen formulas contain zinc oxide nanoparticles (ZnO) and titanium dioxide (TiO2) as mineral UV filters. However, it has been demonstrated that TiO2 and ZnO nanoparticles have anti-microbial properties in vitro. More specifically, Fernand FIÉVET and his team found that at concentrations higher than 1.3 x 103 M, ZnO nanoparticles had bactericidal effects on Escherichia coli. A subsequent study delved deeper into this point, reporting that concentrations higher than 1.6 x 102 M of ZnO would increase the permeability of bacterial membranes, leading to cell death.
Direct research on this subject is, however, still limited and some of these conclusions are theoretical. Studies on human skin are necessary to establish a stance on these results.
Mechanisms are suspected to be responsible for these actions.
Generation of Reactive Oxygen Species (ROS).
When exposed to UV light, nanoparticles of TiO2 and ZnO can generate free radicals, such as hydroxyl radicals and superoxide radicals. These free radicals possess oxidative properties that can damage the cellular membranes of microorganisms, leading to their death.
Release of metallic ions.
ZnO nanoparticles can release zinc ions (Zn2+) into their environment. These ions have anti-microbial properties by disrupting the function of enzymes essential to microorganisms and by causing damage to their DNA, which results in their death.
At Typology, we have made the decision to exclude nanoparticles of ZnO and TiO2 from our sunscreen products, due to the potential risks they pose for skin penetration and ecotoxicity.
Sources
FIÉVET F. & al. Toxicological impact studies based on Escherichia coli bacteria in ultrafine ZnO nanoparticles colloidal medium. Nano Letters (2006).
MCBAIN A. J. & al. Exploring associations between skin, the dermal microbiome, and ultraviolet radiation: advancing possibilities for next-generation sunscreens. Frontiers in Microbiomes (2023).
TASNEEM F.M. & al. A narrative review of the impact of ultraviolet radiation and sunscreen on the skin microbiome. Photodermatology, Photoimmunology & Photomedicine (2023).
LEFRANCOIS C. & al. Fish gut and skin microbiota dysbiosis induced by exposure to commercial sunscreen formulations. Aquatic Toxicology (2024).
