Microplastic in human body - a critical insight into current microplastic research.

BACKGROUND: Microplastics and nanoplastics are ubiquitous environmental contaminants, and human exposure via ingestion and inhalation is increasingly recognized. Numerous studies report microplastics in human tissues and biological fluids, yet the biological relevance and robustness of these findings remain uncertain. This critical work evaluates current evidence on microplastics in the human body, focusing on exposure pathways, particle size relevance, and analytical limitations. Mechanistic data indicate that translocation across intestinal and pulmonary barriers is likely restricted to small microplastics (< 10 µm) and nanoplastics, raising questions about reports of larger particles in human tissues. Key challenges include secondary contamination, size-dependent detection limits, and methodological artifacts associated with common analytical techniques. Experimental evidence for biological effects, including inflammation, microbiome disruption, and cancer-related pathways, is discussed in the context of physiological relevance. AIM: Overall, our work highlights the need for standardized analytical methods, rigorous quality control, and mechanistic studies using realistic exposure scenarios to support sound microplastics related human health research.