Presence of Staphylococcus aureus amplifies zinc oxide nanoparticle toxicity in skin cells

This study examines how Staphylococcus aureus modifies the cellular toxicity of zinc oxide nanoparticles, a common ingredient in sunscreens, cosmetics, and topical products. Using HaCaT keratinocytes, the authors compared exposure to ZnO nanoparticles alone with combined exposure to ZnO nanoparticles and S. aureus. ZnO nanoparticles increased reactive oxygen species production, weakened barrier-related cellular integrity, induced inflammatory signaling, and triggered apoptosis associated with mitochondrial dysfunction. Importantly, the presence of S. aureus significantly intensified these harmful responses, indicating that nanoparticle safety cannot be fully assessed without considering the microbial context of the skin. Mechanistic analyses further showed that MAPK pathway activation contributed to the amplified inflammatory and cytotoxic effects. The findings suggest that ZnO-based formulations may behave differently in healthy skin versus skin colonized or inflamed by S. aureus, providing useful evidence for safer product evaluation and for therapeutic strategies targeting clinically relevant S. aureus-associated skin disorders, including atopic dermatitis and barrier-impaired conditions.