Deciphering the links: Fragmented polystyrene as a driver of skin inflammation.

Nano- and microplastics (NMPs), ubiquitous in the environment, pose significant health risks. We report for the first time a comprehensive study using in-vitro, in-vivo, and ex-vivo models to investigate the penetration and inflammatory effects of fragmented polystyrene (fPS) on human skin, including the analysis of both penetration depth and fPS amounts that penetrate the skin. Human keratinocyte (HaCaT) and human dermal fibroblast (HDF) cells exposed to fPS exhibited notable internalization and cytotoxicity. In a 3D human skin model, fPS particles penetrated the dermal layer within one hour, with an average maximum penetration of 4.7 μg for particles smaller than 2 µm. Similarly, mouse dorsal skin and human abdominal skin models confirmed fPS penetration. RNA sequencing revealed substantial upregulation of inflammatory genes, including IL-1α, IL-1β, IL-18, IL-6, IL-8, ICAM-1, FOS, and JUN, following fPS exposure. These findings were validated at both the mRNA and protein levels, indicating a robust inflammatory response. Notably, the inflammatory response in both the 3D human skin and mouse models increased in a dose-dependent manner, underscoring the toxicological impact of fPS on skin health. This study provides crucial insights into the mechanisms through which NMPs affect human health and underscores the need for further research to develop effective mitigation strategies.