Your skin is home to millions of microorganisms, including bacteria, fungi, and viruses, forming a unique and complex ecosystem that changes based on location.
Some of these microbes, known as commensal bacteria, adapt to their surroundings by feeding on nutrients from the skin and the individual’s lifestyle habits. In return, they produce beneficial compounds, like fatty acids and antimicrobial substances, that influence both their environment and skin health.
Key players, such as Cutibacterium acnes and Staphylococcus epidermidis, play a crucial role in maintaining skin balance and boosting immunity, making them vital for optimal skin health.
It has been demonstrated that microbes residing on the skin influence the immunomodulatory properties of UVR; however, the underlying mechanisms remain to be elucidated.
Scientists discover the body’s protection shield
Researchers have confirmed that certain skin bacteria help protect against UV radiation by breaking down cis-urocanic acid with an enzyme called urocanase. This process enables the skin to adjust its response to sunlight, providing a natural layer of defense.
Researchers employed a combination of advanced techniques, including microbiome sequencing and gnotobiotic mouse models, to investigate how skin bacteria respond to UVB radiation, the type that causes sunburn. They discovered that certain bacteria break down cis-urocanic acid—a UV-absorbing compound—using an enzyme called urocanase.
This process is significant because cis-urocanic acid has a substantial impact on the immune system, influencing how the skin responds to sunlight. By metabolizing it, bacteria limit its ability to suppress immune reactions, effectively fine-tuning how our skin handles UV exposure.
Researchers also highlight an unexpected competition happening on the skin’s surface—sunscreens, cis-urocanic acid, and the microbiome all interact within the outermost layer, shaping how the skin protects itself from the sun.
Preventing ultracold molecules using microwaves
Co-investigator Marc Vocanson, PhD, Centre International de Recherche en Infectiologie, Lyon, France, notes, “This is the first time we have demonstrated a direct metabolic link between UV radiation, a host-derived molecule, and bacterial behavior that affects immune function. As interest grows in both microbiome research and personalized medicine, understanding these microbe-host interactions could reshape the way we think about sun protection, immune diseases, skin cancer, or even treatments like phototherapy.”
Co-investigator Peter Wolf, MD, Research Unit for Photodermatology, Medical University of Graz, Austria, concludes, “These findings open the door to microbiome-aware sun protection, where we not only protect the skin from UV radiation but also consider how resident microbes can alter the immune landscape after exposure. In the future, topical treatments that modulate microbial metabolism could be used to minimize, maintain, or enhance UV-induced immunosuppression when clinically beneficial, such as with phototherapy.”
Commenting on the findings, noted expert in the field Anna Di Nardo, MD, PhD, University of California San Diego, and San Gallicano Dermatological Institute IRCCS, Rome, says, “This pivotal study shows that microbial communities are not passive victims of environmental stress but dynamic regulators of immune responses, capable of metabolizing UV-induced skin products such as cis-urocanic acid.”
“This newly uncovered role of microbial metabolism in modulating UV tolerance reshapes our understanding of the skin barrier — not just as a structural shield but as a metabolically active, microbially regulated interface. With increasing concerns about UV exposure, skin aging, and cancer, a deeper understanding of this axis offers promising avenues for therapy and prevention.”
Journal Reference:
- VijayKumar Patra, Slave Trajanoski, Aaroh Joshi, Vanina Lenief, Chloe Goyet, Altan Cornu, Nicole Golob-Schwarzl, Meghana Somlapura, Amandine Mosnier, Maximilian Zarfl, Thomas Eichmann, Harald Köfeler, Mary Norval, Jean-Francois Nicolas, Peter Wolf, and Marc Vocanson. Urocanase-Positive Skin-Resident Bacteria Metabolize cis-Urocanic Acid and in Turn Reduce the Immunosuppressive Properties of UVR. Journal of Investigative Dermatology. DOI: 10.1016/j.jid.2025.03.035
