Microplastics — fragments smaller than five millimeters — have infiltrated the systems that sustain life. This 2025 review in *Frontiers in Public Health* traces how these synthetic particles move from the environment into the human body, accumulate in organs, and trigger biological damage. Researchers distinguish primary microplastics (produced microscopically, like microbeads and fibers) from secondary ones formed as larger plastics break down. Both bind pollutants such as heavy metals and pathogens that magnify their toxicity. Exposure occurs through inhalation, ingestion, and skin contact — with indoor air often holding the highest concentrations. Inside the body, microplastics provoke oxidative stress and inflammation, disrupt mitochondria, and activate immune pathways like NF-κB and NLRP3, leading to cell damage across organs. They can cross biological barriers, enter the bloodstream, and are linked to neurotoxicity, vascular inflammation, liver fibrosis, and respiratory disease. Their interaction with pollutants and pathogens adds synergistic risks — some particles even carry viral RNA. The authors call for global action: phase out single-use plastics, strengthen wastewater filtration, and promote biodegradable alternatives. They urge standardized detection methods and long-term studies on chronic exposure, especially for vulnerable groups. Public awareness and policy coordination are crucial to reduce human intake and environmental load. Microplastics are no longer just an environmental issue — they are a biological invasion linking ecosystem and human health. Addressing them demands the same urgency as any global public-health crisis. Produced by Cognivault — insight, intelligence, and innovation made clear.