The Sterile Mind: Unravelling the Hygiene Hypothesis, Gut Dysbiosis, and OCD Through Neuroimmunology and Ayurveda

Obsessive-Compulsive Disorder (OCD) is a debilitating neuropsychiatric condition historically conceptualised as an intrinsic corticostriatal neurochemical disorder driven by serotonergic, dopaminergic, and glutamatergic dysregulation. However, the high prevalence of pharmacotherapeutic refractoriness and persistent systemic comorbidities suggest that isolated central nervous system paradigms are insufficient to explain its complex pathophysiology. Emerging evidence indicates that OCD is intimately linked to an evolutionary and immunological mismatch. The Hygiene Hypothesis and the Old Friends Hypothesis establish that modern sanitisation, dietary industrialisation, and urban isolation have depleted ancestral, immunoregulation-inducing symbiotic microflora. This ecological loss impairs regulatory T-cell induction, resulting in unchecked baseline inflammation. Concurrently, disruptions within the bidirectional microbiota-gut-brain axis—marked by epithelial barrier breakdown, metabolic endotoxemia, and the accumulation of pro-inflammatory microbial metabolites such as succinic acid—drive sustained neuroinflammation within the cortico-striato-thalamo-cortical (CSTC) circuit. Positron emission tomography targeting the 18-kDa translocator protein (TSPO) confirms active microgliosis across the striatum and orbitofrontal cortex in affected individuals. Remarkably, classical Ayurvedic medicine conceptualised psychopathology through an analogous gut-brain continuum millennia ago. Classified within Manasa Roga under the diagnostic category of Atattvabhinivesha ("clinging to the unreal"), obsessive loops are understood as the clinical consequence of Mandagni (suppressed metabolic and digestive fire) generating Ama (systemic endotoxins). These circulating toxins penetrate the Manovaha Srotas (mental cognitive channels), derange Prana Vayu, Sadhaka Pitta, and Tarpaka Kapha, and deplete Ojas (neuroimmune vigour and resilience), ultimately collapsing Dhriti (cognitive and motor inhibition). This review provides a comprehensive synthesis of contemporary neuroimmunology, microbial metabolomics, and classical Ayurvedic literature to establish a translational paradigm for OCD. Multi-target therapeutic interventions—incorporating Medhya Rasayanas, barrier-restoring botanicals such as Triphala, Panchakarma bio-purification, circadian alignment, and the cognitive restructuring of Sattvavajaya Chikitsa—are evaluated as systematic strategies to restore microbial diversity, attenuate CSTC neuroinflammation, and re-establish cognitive flexibility.