@article {Marianotobaccocontrol-2020-056393, author = {Lorena C. Mariano and Saman Warnakulasuryia and Kurt Straif and Lu{\'\i}s Monteiro}, title = {Secondhand smoke exposure and oral cancer risk: a systematic review and meta-analysis}, elocation-id = {tobaccocontrol-2020-056393}, year = {2021}, doi = {10.1136/tobaccocontrol-2020-056393}, publisher = {BMJ Publishing Group Ltd}, abstract = {Objectives Inhalation of secondhand smoke (SHS) causes several diseases, including lung cancer. Tobacco smoking is a known cause of oral cancer; however, it has not been established whether SHS also causes oral cancer . The aim of this study was to evaluate the potential association between SHS exposure and the risk of oral cancer.Methods A systematic review and meta-analysis study (following the PRISMA guidelines) was developed to examine the studies reporting on the associations of SHS and the risk of oral cancer, employing a search strategy on electronic databases (PubMed, Web of Science, Scopus, Cochrane Library, Open Grey, and ProQuest databases for dissertations) until 10 May 2020. Meta-analyses and sensitivity analyses were performed using random-effect models. The protocol was registered in PROSPERO (CRD42020189970).Results Following the application of eligibility criteria, five studies were included, comprising a total of 1179 cases and 5798 controls, with 3452 individuals exposed and 3525 individuals not exposed to SHS. An overall OR of 1.51 (95\% CI 1.2o to 1.91, p=0.0004) for oral cancer was observed, without significant heterogeneity (I2=0\%, p=0.41). The duration of exposure of more than 10 or 15 years increased the risk of oral cancer (OR 2.07, 95\% CI 1.54 to 2.79, p\<0.00001), compared with non-exposed individuals, without significant heterogeneity (I2=0\%, p=0.76).Conclusions This systematic review and meta-analysis supports a causal association between SHS exposure and oral cancer. Our results could provide guidance to public health professionals, researchers, and policymakers to further support effective SHS exposure prevention programs worldwide.}, issn = {0964-4563}, URL = {https://tobaccocontrol.bmj.com/content/early/2021/03/18/tobaccocontrol-2020-056393}, eprint = {https://tobaccocontrol.bmj.com/content/early/2021/03/18/tobaccocontrol-2020-056393.full.pdf}, journal = {Tobacco Control} }