They have a severe impact on your health.
The bad news just keeps pouring in for e-cigarette smokers, after a study last week found that they do damage to smokers' DNA and
increase the risk of heart disease and cancer.
Scientists have now warned that flavouring chemicals and liquids used in the devices are toxic to white cells in our blood.
Research into which particular flavours are most harmful to smokers found that cinnamon, vanilla and butter are the worst. But, on top of that, mixing e-cig flavours - much like mixing drinks on a night out - has the strongest impact on your health.
The chemicals can cause inflammation to monocytes – the white blood cells in the immune system that combat bacteria and viruses.
The study,
published in the journal Frontiers in Physiology, is yet another investigation that has reached the conclusion vaping has harmful consequences for users.
Dr Thivanka Muthumalage, of Rochester University said: "Cinnamon, vanilla and butter flavouring chemicals were the most toxic but our research showed mixing flavours of e-liquids caused by far the most toxicity to white blood cells."
It comes after researchers tested the effects of e-cigarettes on mice, and human lung and bladder cells.
In those tests, mice breathing the e-cigarette vapour showed greater damage to their DNA in the heart, lungs and bladder, as well as being more likely to develop tumours compared to the control group of mice breathing filtered air. Meanwhile cultured human cells reacted in a similar manner when exposed to nicotine and its derivatives.
