Background: Microplastics (MPs, < 5 mm) and nanoplastics (NPs, 1-1,000 nm) – collectively referred to as MNPs – have become pervasive environmental contaminants. Their potential accumulation in the human body, particularly in the brain, has raised significant health concerns.

Objective: This review summarizes current evidence on the presence of MNPs in the brain, their potential routes of entry, mechanisms of action, and implications for neurological health.

Methods: We performed a critical review of recent literature concerning MNP exposure, uptake pathways, distribution in human tissues, especially the brain, and their neurotoxic effects, with a focus on developmental vulnerability.

Results: MNPs can reach the brain through ingestion, inhalation, and possibly via the bloodstream, crossing the blood-brain barrier (BBB) through mechanisms such as endocytosis, pinocytosis, or via immune cells. Animal studies suggest accumulation of MNPs in the brain induces oxidative stress, neuroinflammation, and behavioral changes. Particularly concerning is the perinatal period, where multipotent stem cells in breast milk may act as vectors of MNPs and endocrine-disrupting chemicals (EDCs) into the neonatal brain.

Conclusions: MNPs represent an emerging threat to neurodevelopmental health. Future research must clarify the long-term effects of MNP exposure, especially in early life, and identify potential strategies to mitigate their impact. The irony lies in the semantic shift: while “plasticity” once symbolized the brain’s capacity for change, “plastic” now threatens that very adaptability.