Microplastics and nanoplastics are persistent environmental contaminants of increasing relevance to human health, particularly because ingestion places the gastrointestinal tract at the center of exposure. In inflammatory bowel disease (IBD), in which epithelial barrier dysfunction, dysbiosis, immune activation, and environmental factors intersect, these particles represent a biologically plausible but incompletely characterized exposure. This narrative review summarizes the current evidence on microplastics, intestinal inflammation, and IBD, including exposure routes, particle definitions, measurement challenges, biological mechanisms, experimental data, and human studies. Experimental evidence suggests that microplastics may disrupt the mucus–epithelial barrier, promote oxidative stress, alter microbial and metabolite profiles, and amplify inflammation in susceptible or inflamed intestinal environments. Human evidence remains limited and observational, with fecal, serum, and tissue-based studies reporting associations between microplastic burden and IBD-related features, including disease activity, fecal calprotectin levels, and fibrostenotic tissue changes. Current data do not establish microplastics as causal drivers of IBD or clinically useful biomarkers. The most balanced interpretation is that they may act as environmental disease modifiers or markers of altered intestinal handling rather than as primary initiators of IBD. Standardized analytical methods and longitudinal human studies are needed to clarify their clinical relevance.