Conclusion This animal study has shown that the vapour from e-cigarettes contains free radicals, which are toxic to cells and are linked to cancer. Exposure to e-cigarettes caused inflammation in the lungs of mice, with increased numbers of macrophages, which mop up damaged and dead cells. Mice exposed to e-cigarette smoke also had a reduced ability to fight both bacterial and viral infections. Taken together, this is convincing evidence suggesting that e-cigarettes are not harmless. However, the effect of e-cigarettes was not compared to normal cigarettes in this study, so it is not clear how much safer they might be. The study was also not conducted in humans. An animal study such as this can give us a good idea of the effects that a chemical could have in humans. However, mice and human...