Microplastics and inflammatory bowel disease: dissecting the evidence from observational links to potential causal mechanisms.

Inflammatory bowel disease (IBD) has surged globally, and environmental factors such as microplastics (MPs) have emerged as potential contributors alongside a complex interplay between altered gut microbiota and dysregulated immune response in genetically susceptible individuals. While current evidence linking MPs to intestinal inflammation remains largely associative, a causal relationship between MP exposure and IBD in humans has yet to be confirmed. Therefore, this review aims to summarize current evidence regarding the occurrence, detection, and potential pathogenic roles of MPs in IBD. Emerging evidence suggests that MPs disrupt gastrointestinal integrity and immune homeostasis through multiple pathological mechanisms. MPs physically compromise the intestinal barrier by downregulating key tight junction proteins such as ZO-1 and claudin-1, altering endocytosis, and inducing oxidative stress. Concurrently, MPs induce gut microbial dysbiosis, often reflected by a reduced Firmicutes/Bacteroidetes ratio, depletion of commensal taxa, and overgrowth of proinflammatory bacteria, including Escherichia coli, Bilophila wadsworthia, and Ruminococcus gnavus. These changes trigger proinflammatory cascades and exacerbate mucosal damage, processes that are closely linked to the pathophysiology of IBD. Current detection of MPs in stool and colon tissue samples from individuals with IBD commonly relies on a combination of microscopic (e.g., optical microscopy) and spectroscopic (e.g., Fourier-transform infrared spectroscopy or Raman spectroscopy) approaches. These approaches enable the identification and characterization of MPs within biological matrices. In summary, this review explores the potential pathogenic mechanisms linking MPs to IBD, providing insights that support a possible causal relationship and highlighting a novel, underexplored environmental factor in disease onset and progression.