Microplastics in Humans: A Critical Review of Biomonitoring Evidence and Immune–Metabolic Associations

Microplastics in the human body pose a significant health challenge due to their potential impact on the immune system and metabolic processes. This review summarises and critically evaluates current evidence regarding the detection of microplastics in human tissues and biological fluids, as well as their potential biological mechanisms of action. Published studies were examined with particular attention to methodological diversity, analytical techniques, and differences in study design. The review highlights consistent observations of microplastic presence in human organs, including the placenta, blood, and lungs, while also revealing significant variability in detection methods and exposure assessment. Evidence suggests that microplastics may have a potential impact on immune functions, including the modulation of the immune response, the risk of autoimmunity and immunosuppression, and metabolic homeostasis disorders that affect hormone regulation, glucose, and lipid levels. Despite the growing number of studies, major gaps include the lack of standardised analytical protocols, limited long-term human data, and insufficient mechanistic understanding at the molecular level. Addressing these gaps is crucial for enhancing risk assessment and developing effective preventive strategies to minimise human exposure to microplastics and safeguard public health.