The harm of E-cigarettes cannot be underestimated. In vivo and in vitro evidence has confirmed that the components contained are harmful to the respiratory system and the cardiovascular system. Moreover, the levels of harmful components, which include volatile organic compounds, tobacco-specific nitrosamines, and heavy metals, in E-cigarettes are higher than those in traditional cigarettes. At present, the research on E-cigarettes is fragmentary and incomplete, and there has been no systematic review of its safety. Additionally, the lack in quality control and authorized policies for E-cigarettes makes it inconvenient to conduct further research and development.