For the carbonyl compounds, the heating of glycerol will produce harmful aldehydes related to temperature, including formaldehyde, acetaldehyde and acrolein. These three compounds were identified in almost all of the examined E-cigarettes . The study of Gassee, F.R. et al. showed that the mixture of the above three compounds produced more sensory stimuli than those of a single compound . Among them, formaldehyde was categorized as a Class 1 carcinogen in 2006. Acrolein stimulates the nasal cavity, damages the lungs and the inner walls of the blood vessels, and is a major factor leading to cardiovascular disease. Chronic inhalation of acrolein inhibits circulation of endothelial progenitor cells and promotes atherosclerosis, which accelerates the rate of hardening of the aorta by 1.6 times . Ambrus, J.L. et al. also confirmed the presence of acrolein, toxic substances and mutagenic compounds in E-cigarette smoke. It was found that the carcinogenic metabolic enzymes in rats exposed to E-cigarette smoke increased significantly, inducing a greater carcinogenic risk of carcinogens in E-cigarette smoke .