A 30-s exposure to ethanol 20% is cytotoxic to human keratinocytes: possible mechanistic link between alcohol-containing mouthwashes and oral cancer.

OBJECTIVES: To provide mechanistic evidence for the epidemiological link between long-term use of alcohol-containing mouthwashes and oral cancer.

MATERIAL AND METHODS: Human epithelial keratinocytes were exposed for 30 s to concentrations of ethanol commonly present in mouthwashes. After a recovery period, cell viability was assessed with the MTT assay.

RESULTS: A marked cytotoxic effect was observed for ethanol concentrations of 20% and above.

CONCLUSIONS: The cytotoxicity of ethanol may explain the epidemiological association between mouthwash use and oral cancer. Evidence suggests that the risk of developing cancer in a tissue is strongly determined by the number of stem cell divisions accumulated by the tissue during a person's lifetime; cell division is a major source of mutations and other cancer-promoting errors. Since cell death activates the division of stem cells, the possible cytotoxicity of ethanol on the cells lining the oral mucosa will promote the division of the stem cells located in deeper layers to produce new cells to regenerate the damaged epithelium. If we regularly use mouthwashes containing cytotoxic concentrations of ethanol, the stem cells of the oral cavity may need to divide more often than usual and our risk of developing oral cancer may increase.

CLINICAL RELEVANCE: Many mouthwashes contain percentages of ethanol above 20%. Because ethanol is not crucial to prevent and reduce gingivitis and plaque, members of the dental team should consider the potential risk of oral cancer associated with frequent use of alcohol-containing mouthwashes when advising their patients.