This study investigated the levels of four groups of potentially toxic and carcinogenic compounds in vapor from 12 brands of e-cigarettes and a reference product, the medicinal nicotine inhaler. The compounds analyzed included carbonyls, volatile organic compounds (VOCs), tobacco-specific nitrosamines (TSNAs), and metals. The study aimed to assess the potential health risks associated with e-cigarette vapor and compare them to those of conventional cigarette smoke. The results showed that e-cigarette vapor contained some toxic substances, with levels ranging from 9 to 450 times lower than in cigarette smoke. In many cases, the levels were comparable to trace amounts found in the reference product. Carbonyl compounds such as formaldehyde, acetaldehyde, and acrolein were detected in e-cigarette vapor. VOCs like toluene and m,p-xylene were also found, though at lower levels. TSNAs, including N'-nitrosonornicotine (NNN) and 4-(methylonitrosoamino)-1-(3-pirydylohe-1-butanone (NNK), were detected in some e-cigarette vapors. Metals such as cadmium, nickel, and lead were also identified in e-cigarette vapor. The study found that while e-cigarette vapor contains some toxic substances, the levels are significantly lower than those in cigarette smoke. This suggests that e-cigarettes may be a less harmful alternative to conventional cigarettes for reducing exposure to tobacco-specific toxicants. However, further research is needed to fully understand the long-term health effects of e-cigarette use and to determine whether they can be effectively used as a harm reduction strategy for smokers who are unable to quit. The study also highlights the need for more comprehensive research on the chemical composition of e-cigarette vapor and its potential health impacts.This study investigated the levels of four groups of potentially toxic and carcinogenic compounds in vapor from 12 brands of e-cigarettes and a reference product, the medicinal nicotine inhaler. The compounds analyzed included carbonyls, volatile organic compounds (VOCs), tobacco-specific nitrosamines (TSNAs), and metals. The study aimed to assess the potential health risks associated with e-cigarette vapor and compare them to those of conventional cigarette smoke. The results showed that e-cigarette vapor contained some toxic substances, with levels ranging from 9 to 450 times lower than in cigarette smoke. In many cases, the levels were comparable to trace amounts found in the reference product. Carbonyl compounds such as formaldehyde, acetaldehyde, and acrolein were detected in e-cigarette vapor. VOCs like toluene and m,p-xylene were also found, though at lower levels. TSNAs, including N'-nitrosonornicotine (NNN) and 4-(methylonitrosoamino)-1-(3-pirydylohe-1-butanone (NNK), were detected in some e-cigarette vapors. Metals such as cadmium, nickel, and lead were also identified in e-cigarette vapor. The study found that while e-cigarette vapor contains some toxic substances, the levels are significantly lower than those in cigarette smoke. This suggests that e-cigarettes may be a less harmful alternative to conventional cigarettes for reducing exposure to tobacco-specific toxicants. However, further research is needed to fully understand the long-term health effects of e-cigarette use and to determine whether they can be effectively used as a harm reduction strategy for smokers who are unable to quit. The study also highlights the need for more comprehensive research on the chemical composition of e-cigarette vapor and its potential health impacts.