The growing prevalence of micro- and nanoplastics (MNPs) in the environment elicits concerns about their possible impact on human neurological health. Although studies on animals have suggested neurotoxic effects, evidence from humans is still scarce. This systematic review gathers existing human data to assess the presence, types, detection techniques, and neurological consequences of MNPs in different biological matrices. A comprehensive review was performed on peer-reviewed research concentrating on human studies that report the detection of MNPs in biological tissues and fluids. Four qualifying studies were identified: one clinical observational study, two cadaveric analyses, and one quasi-experimental trial. The data collected encompassed demographics, detection methods, types and concentrations of polymers, biological matrices examined, and neurological biomarkers. MNPs were observed in cerebrospinal fluid (CSF), faeces, urine, olfactory bulbs (OBs), and in brain, liver, and kidney tissues from postmortem cases. The polymers that were reported most frequently were polyethylene (PE) and polypropylene (PP). The detection methods included micro-Fourier transform infrared spectroscopy (µFTIR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), laser direct infrared imaging (LDIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Although the available evidence is limited, emerging findings indicate the possible accumulation of MNPs in the human central nervous system (CNS), particularly in individuals with dementia or compromised blood-brain barrier (BBB) integrity. Relationships were noted between MNP exposure and disruptions in the BBB, inflammatory markers, and alterations in the gut-brain axis. This review consolidates the findings and emphasizes the need for further exploration of human exposure to MNPs and their possible accumulation in neural tissues. Although there is variability in methodologies used in the reviewed articles, PE and PP stand out as the primary polymers of concern. While a direct causal relationship cannot yet be confirmed, the results highlight the necessity for improved detection methods, larger sample sizes, and long-term studies to better understand the impact of MNPs on neuroinflammation and neurodegeneration.
