Adverse effects of electronic cigarettes on human health.

Many people have associated e-cigarettes with adjectives such as trendy and cool, and regarded vaping as "a safer alternative to cigarette smoking". Compared with the conventional cigarettes, the public is less familiar with the dangers of e-cigarettes. E-cigarettes produce an aerosol by heating the e-liquid (usually comprising nicotine, flavorings, propylene glycol, vegetable glycerin, and other additives). Harmful substances are generated during the vaporization, such as formaldehyde. Cellular damages and DNA hypermethylation are also found to be associated with vaping. We reviewed the clinical neoplastic cases of patients with vaping history (three oral squamous cell carcinomas, one conjunctival squamous intraepithelial neoplasia, and one thoracic NUT-midline carcinoma). These patients tend to be younger than the average cancer patients. Although the exact relations between the cellular damages or DNA hypermethylation and vaping still need further investigations, we should be very careful about the dangers of using e-cigarettes as aids for cigarette smoking cessation.