"This report is refreshing because it puts the hazards of vaping into context, depending on whether people are vaping to quit smoking, or are vaping just for its own sake.

"A limitation is that the absolute amount of vaping-associated cancer risk still remains unclear. I think we help people as scientists when we give more than one point of reference for things, like long term cancer risk, that are otherwise unseen. An example is cancer risk from exposure to medical radiation. Organisations like the US Department of Energy have made useful resources that put this risk into context, by comparing it to commonplace things including air travel, building materials, soil, our own bodies, cosmic radiation, and radon gas. I think the communication of hazards of vaping will be improved if we can do something similar. How do risks of vaping compare to everyday things like indoor gas cooking, barbecue food, alcohol, and sugary drinks?

"The main problem with vaping nicotine in my view is that it is addictive and this in turn is allowed to be profitable. I worry that physical hazards of vaping can be a distraction from the underlying cycle of addiction and profit. Any work that puts hazards of vaping into context will raise the level of the public conversation. I became interested in vaping because of my work as an oncologist for lung cancer, that remains overwhelmingly caused by smoking cigarettes, that are still many times more dangerous than vaping."

"This study extends our knowledge in relation to the role of vapes in tobacco control policy. Vapes are often framed as universal ‘harm reduction’ products, however the authors remind us that their impact is relative to who is using them.

"For people who smoke, vapes may help them to quit their nicotine addiction completely or at least switch to vapes. However, simply because vapes are available, a proportion of those who ‘switch’ might have otherwise quit their addiction. In this case they may be exposed to more harm.

"Importantly, young people make up a large proportion of people taking up vapes, and a large proportion have never smoked. Our rates of vaping among young people are very high compared to other countries. The authors conclude that vaping is likely to expose people who have never smoked to carcinogens. However, they also note that vapes are still relatively new and we do not yet have a full understanding of any cancer risks. Given their conclusions it is evident that much improved protections are needed for people who have never smoked from taking up vaping, in particular young people.

"Given we still do not know the impact of vapes on health, a cautionary approach is needed as to their role, if any, in tobacco control. We also need to move away from their promotion as ‘lifestyle’ products that promotes harmful use.”

"It will take many years to collect clinical data to determine whether vaping causes cancer because it takes at least 15-years for cancers to develop after exposure to cancer-causing chemicals.

"In our paper, we used knowledge of the chemistry of the vaping process to determine the chemical composition of ‘vape smoke’ and then assessed the carcinogenic risk of each of the ‘vape smoke’ chemicals from published animal and other toxicity studies. From this, we predicted the cancer risk to vapers based on the published levels of these chemicals in ‘vape smoke’ and concluded that vaping presents a cancer risk.

"However, it is likely that the vaping cancer risk is lower than the cigarette smoking cancer risk. Therefore, using vaping for smoking cessation is acceptable because this will lower the overall cancer risk, but vaping for its own sake adds to life’s cancer risks and is therefore unacceptable."