Pathophysiology of Chronic Pain

OBJECTIVES: Chronic pain affects 1 in 5 people and persists because protective nociception is converted into maladaptive neural, immune, and psychological states. This review aimed to consolidate mechanistic and clinical evidence to clarify that transformation and identify leverage points for durable relief. METHODS: Following the Scale for the Assessment of Narrative Review Articles (SANRA) guidance, we conducted a narrative review of articles published January 1, 2000 to June 30, 2025 accessing PubMed, Embase, Web of Science, Scopus, CINAHL, PsycINFO, and the Cochrane Library, supplemented by gray literature. Eligible studies explored biological, immunologic, genetic, epigenetic, or psychosocial mechanisms or tested mechanism-targeted interventions. Data were thematically synthesized and appraised for methodological quality. RESULTS: Convergent findings reveal a multistage cascade: peripheral sensitization driven by aberrant ion channels and inflammatory mediators; spinal and supraspinal sensitization sustained by glial activation and loss of inhibition; and large-scale cortical and limbic reorganization that embeds pain within memory and emotion circuits. Neuroimmune dialogue, microbiome dysbiosis, sex-specific responses, and environment-induced epigenetic changes amplify these processes, while psychological stress and social adversity modulate their expression. Mapping these mechanisms to neuropathic, nociceptive, and nociplastic syndromes highlights therapeutic windows exploited by emerging agents such as calcitonin gene-related peptide antibodies, chemogenetic nociceptor silencing, closed-loop neuromodulation, targeted cytokine blockade, and microbiota modulation. Biomarker-informed precision approaches promise to replace empirical prescribing. DISCUSSION: Synthesizing cross-disciplinary evidence positions chronic pain as a systems disease requiring integrated, mechanism-based, and person-centered care. Defining the shared biological scaffold clarifies why traditional symptom-focused treatments frequently fail and outlines research priorities for disease-modifying analgesics and equitable delivery models.