The e-liquid of the E-cigarette is usually a liquid mixture of propylene glycol, glycerin, nicotine, essence and some other chemical substances. E-cigarette sellers have always packaged E-cigarettes as harmless smoking-cessation products or cigarette substitutes without harmful substances such as tar, carbon monoxide, suspended particles, etc. However, up to now, the research about the safety of E-cigarettes has been scarce, and there is no systematic review focusing on the safety assessment of E-cigarettes worldwide . In particular, it is still unclear whether aerosols produced by electronic smoke do harm to our health. Furthermore, it’s controversial that E-cigarettes emit only harmless steam . Although more and more research shows that the known dangers of electronic smoke are much smaller than for traditional cigarettes, it is uncertain how dangerous the potential toxic effects of E-cigarettes are.