There are studies that have investigated the cytotoxicity of the essence in E-cigarettes. Bahl, V. et al. used MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide) assays to test the cytotoxicity of e-liquids. The results showed that some e-liquids were cytotoxic to human embryonic stem cells and mouse neural stem cells, and that the composition and concentration of chemical components played an important role. In addition, more evidences confirmed that the chemical properties and the concentration of essence added to the e-liquid, rather than the nicotine alone, are much more harmful . Farsalinos, K.E. et al. used MTT tests to study the in vitro toxicity of the e-liquid of 20 E-cigarettes. The results showed that some electronic smoke liquid had a toxic effect on cardiac muscle cells after heating and atomizing, which would cause disease. The evidence indicated that the ingredients involved in the progress of diseases were related to the production process adopted by the liquid tobacco production company, as well as the flavor components added to cater to the public’s preference . Cinnamylaldehyde and diacetyl are approved flavorings in food, but they will affect people’s health when inhaled . Zeng, W.L. et al. collected tobacco smoke by cell culture medium, and studied the effect of smoke on the relative proliferation rate of Chinese hamster ovary cells (CHO cells) by MTT. The results showed that the relative proliferation rate of flue gas trapping liquid on CHO cells was 10 times higher than that of a 3R4F-reference-cigarette at 100% smoke concentration .