Experiments conducted on mice and cultured human cells show that nicotine in e-cigarette vapors may cause changes in the DNA that may elevate cancer risk.
Researchers, headed by Professor of Epidemiology and Medical Statistics, Alan Hacsuos, of the University of London School of Cardiology (UCL), who published the publication in the British medical journal, studied (meta-analysis) the findings of 141 investigations 1946-2015 and calculated the risk of smoking one, five or 20 cigarettes.
Now there were 18 million e-cigarette smokers in the U.S. and 16% of high school students used the devices, said the researchers. However, the results of this study may take several years to determine.
Scientists have warned that vaping devices - considered by many to be a healthier alternative to tobacco - could damage to your DNA and increase the risk of heart disease and cancer.
The main cancer risk with tobacco cigarettes is caused by the release of a number of carcinogenic compounds when they are burned and inhaled.
About one in 20 people in the United Kingdom has adopted a vaping habit as a markedly safer alternative to smoking tobacco.
At the same time, the report also found that their use among younger people increased the risk of them taking up conventional smoking when they're older. They also exposed the mice to nicotine and solvents separately.
This is avoided in e-cigarettes, with nicotine delivered through aerosols without burning tobacco. This amounted to what Hajek called "extremely large doses of nicotine".
To begin the study, the researchers tested how known cancer-causing chemicals found in regular cigarettes damaged a DNA sample. It also retarded DNA fix functions and proteins in the lungs.
Tang went on to look at human lung and bladder cells and found that exposing the cells to nicotine and its breakdown products made the cells turn into tumour tissue more easily.
Some experts not involved in the study aren't so enthusiastic about the findings.
"Up to two-thirds of long term smokers will die due to their addiction, but e-cigarettes don't contain tobacco".
It's the first evidence we have that nicotine can be carcinogenic in and of itself, said Dr Roy Herbst, chief of medical oncology at Yale Cancer Centre, and chair of the American Association for Cancer Research's Tobacco and Cancer sub-committee.
"Research in people has shown that those who make a complete switch from smoking tobacco to e-cigarettes can significantly reduce their exposure to key harmful chemicals in tobacco smoke".