The global proliferation of plastic materials has led to an unprecedented accumulation of microplastics and nanoplastics in natural ecosystems, with growing evidence indicating their pervasive presence within the human body. Recent advancements in analytical detection have confirmed microplastics in human blood, lung tissue, liver tissue, and other biological matrices, raising profound concerns regarding their potential health implications. This article presents a comprehensive and theoretically grounded examination of human exposure to microplastics, focusing on environmental sources, exposure pathways, internal distribution mechanisms, detection methodologies, and emerging toxicological evidence. Drawing strictly on peer-reviewed references, this work synthesizes atmospheric, dietary, and occupational exposure routes, while critically examining the physicochemical properties of microplastics that influence bioavailability and biological persistence. Particular emphasis is placed on analytical challenges in detecting microplastics in complex human samples, including the application of μFTIR, GC-MS pyrolysis, and nanoparticle tracking analysis. The article further explores mechanistic insights into tissue translocation, inflammatory responses, oxidative stress, reproductive toxicity, and potential synergistic effects with co-exposed pollutants such as metals and metalloids. By integrating findings from environmental science, toxicology, and biomedical research, this study highlights critical knowledge gaps, methodological limitations, and future research priorities essential for understanding the long-term implications of microplastic exposure on human health. The analysis underscores the urgent need for standardized definitions, harmonized methodologies, and interdisciplinary approaches to accurately assess risk and inform public health policy.