Impact of Electronic Cigarette Use on the Oral Microbiota: A Systematic Review

AIM: To examine whether the oral microbiota of e-cigarette users differs from that of never smokers and current smokers. MATERIALS AND METHODS: PubMed, Scopus and Web of Science were searched on 27 August 2025. Human studies using molecular methods to compare oral microbiota in saliva, subgingival plaque and oral mucosal swabs among e-cigarette users, never smokers and current smokers were included. Primary outcomes were alpha diversity, beta diversity and differential taxonomic abundance. Risk of bias was assessed using JBI tools and certainty of evidence using GRADE. RESULTS: Twelve studies were included; most were cross-sectional and heterogeneous in design, exposure and samples. Alpha diversity findings were inconsistent across samples, whereas beta diversity more consistently indicated distinct microbial communities in e-cigarette users compared with never smokers and current smokers. Taxonomic differences were heterogeneous and sample-dependent, with some enrichment of genera such as Veillonella, Leptotrichia, and Fusobacterium compared with never smokers. CONCLUSIONS: Electronic cigarette use is associated with sample-specific oral microbiota differences that partly overlap with, but differ from, those observed in never smokers and current smokers. However, the certainty of evidence is very low due to predominantly cross-sectional designs and methodological limitations, underscoring the need for longitudinal studies with standardised exposure and protocols.