The oral cavity contains a complex and dynamic microbial ecosystem that plays a central role in maintaining both local and systemic homeostasis. Emerging evidence indicates that disturbances in oral microbial communities-including genetic and functional diversity within species-are associated not only with oral diseases but may also contribute to the development and progression of systemic diseases. This narrative review summarises the current state of knowledge on bidirectional interactions between oral microbial communities and major organ systems. A comprehensive search of PubMed/MEDLINE, Web of Science, Scopus, and Cochrane databases was conducted for studies published between 2019 and 2025, prioritising systematic reviews, meta-analyses, and high-quality mechanistic studies. Ultimately, 40 articles were included in the narrative synthesis. The results provide clear evidence of an association between oral dysbiosis and cardiovascular disease (CVD), type 2 diabetes mellitus (T2DM), chronic respiratory infections, and adverse pregnancy outcomes (APOs). Recent data also suggest links with neurodegenerative disorders, chronic kidney disease (CKD), autoimmune diseases, and cancer. Proposed mechanisms include transient or persistent bacteraemia, systemic inflammation caused by microbial metabolites and endotoxins, disruption of immune homeostasis, molecular mimicry, and modulation of host metabolic pathways. Despite growing evidence linking oral microbial communities to systemic health, most findings are based on observational studies, and causal relationships remain to be established through longitudinal and interventional research. Understanding the connection between the mouth and the body highlights the potential for targeting oral microbial activity, virulence factors, and host inflammatory responses in disease prevention and treatment.

Secukinumab (SEC) is a recombinant, fully human monoclonal antibody that is selective for interleukin-17A (IL-17A). SEC may increase the risk of developing infections such as oral herpes and oral candidiasis. The aim of this case report and literature review was to describe chronic hyperplastic candidiasis (CHC) in a patient with psoriasis (PsO) and psoriatic arthritis (PsA) treated with SEC. CHC is a rare and atypical clinical entity. A definitive diagnosis requires biopsy of the oral mucosa for histopathological diagnosis (PHD). The differential diagnosis includes hairy tongue, hairy leukoplakia, oral lichen planus (OLP), oral lichenoid reaction (OLR), leukoplakia, frictional keratosis, morsication, oral psoriasis, syphilis, and oral lesions associated with coronavirus disease (COVID-19). In addition to the usual factors (xerostomia, smoking, antibiotics, vitamin deficiency, immunosuppression, comorbidities), the new biological therapies/immunotherapies are a predisposing factor for oral candidiasis. The therapeutic approach must be multidisciplinary and in consultation with a clinical immunologist. Dentists and specialists (oral medicine, dermatologists, rheumatologists) must be familiar with the oral adverse events of the new biological therapies. Simultaneous monitoring of patients by clinical immunology and oral medicine specialists is crucial for timely diagnosis and therapeutic intervention to avoid possible adverse events and improve quality of life (QoL).