The role of probiotics and prebiotics in preventing and treating oral mucositis caused by chemoradiotherapy: a narrative review

Oral mucositis (OM) is a frequent and debilitating toxicity of anticancer therapy, particularly chemotherapy, radiotherapy, and chemoradiotherapy, and may cause severe oral pain, dysphagia, nutritional compromise, secondary infection, reduced quality of life, and treatment interruption. OM is not only a superficial epithelial injury; its pathogenesis involves direct cytotoxic damage to rapidly dividing basal epithelial cells, oxidative stress, inflammatory signaling activation, cytokine-mediated amplification, mucosal barrier disruption, ulceration, and delayed epithelial repair. Increasing evidence also indicates that anticancer therapies can disturb the oral microbial ecosystem, leading to oral dysbiosis that may amplify local inflammation and impair mucosal recovery. In addition, gut-immune and gut-oral interactions may contribute indirectly to mucosal inflammation, especially in patients receiving systemic chemotherapy or multi-strain gut-directed probiotic interventions. These mechanisms provide a biological rationale for investigating probiotics, prebiotics, and synbiotics as microbiome-targeted supportive strategies for OM. This narrative review summarizes current mechanistic and clinical evidence on probiotics, prebiotics, and synbiotics for the prevention and management of cancer therapy-induced OM, with emphasis on oral microbiome modulation, inflammatory regulation, epithelial barrier protection, immune-related pathways, clinical efficacy, safety considerations, and evidence limitations. Available studies suggest that selected probiotic regimens may reduce OM severity in specific settings, particularly head and neck radiotherapy/chemoradiotherapy and nasopharyngeal carcinoma chemoradiotherapy. However, findings remain heterogeneous because of differences in strain selection, formulation, dose, route, intervention duration, cancer type, treatment regimen, oral-care comparator, and OM grading system. Evidence for prebiotics and synbiotics is more limited and often indirect. Therefore, microbiome-targeted interventions should currently be considered promising adjunctive supportive strategies rather than standardized therapies. Larger randomized trials with standardized OM grading, oral microbiome profiling, mechanistic biomarkers, and predefined safety monitoring are required before routine clinical recommendations can be established.