The main difference between e-cigarettes and smoking tobacco is that there is no combustion (burning) involved with e-cigarettes. It is the burning of tobacco that is the cause of preventable tobacco related mortality and morbidity.

Because of this, the current expert estimate is that using e-cigarettes is about 95% less harmful than smoking cigarettes.

E-cigarettes are devices that deliver nicotine within an inhalable aerosol by heating a solution that typically contains nicotine, propylene glycol and/or glycerol, plus flavours.

This aerosol is commonly referred to as vapour and so the use of an e-cigarette is often described as vaping.

Safety
E-cigarettes are considerably less harmful than smoking because they do not involve the burning of tobacco. In this short film clip Professors Robert West and John Britton summarise what we know about the safety of e-cigarettes.

Most things that we do carry some risk and so it is unlikely that we will ever be able to say that e-cigarettes are completely safe.

However, when considering the safety of e-cigarettes we need to take into account that virtually all e-cigarette users are either current or ex-smokers. It is therefore more appropriate to ask the question: how much less harmful than smoking are e-cigarettes?

“Best estimates show e-cigarettes are 95% less harmful to your health than normal cigarettes.”
Duncan Selbie, Chief Executive, Public Health England

Short-term exposure to e-cigarettes appears to pose few if any risks. Mouth and throat irritation are the most commonly reported symptoms and these subside over time. There are no high quality safety data from long-term e-cigarette use, but there is no good reason to expect that their use would be anywhere near as risky as smoking.

There is no evidence of harm to bystanders from exposure to secondhand e-cigarette vapour and any risks are likely to be extremely low. The vapour contains a small fraction of the toxicants in tobacco smoke and dissipates very quickly into the ambient air.

Role of e-cigarettes
There are a number of reasons that smokers and ex-smokers give for using e-cigarettes: to quit smoking, save money, protect others from secondhand cigarette smoke, help deal with situations when unable to smoke, give it a try, help reduce the amount of tobacco smoked but not stop completely and prevent relapse back to smoking after quitting.

These reasons suggest three main roles for e-cigarettes:

Quitting
This involves making the switch from smoking cigarettes to using an e-cigarette. E-cigarette use for quitting can be for a relatively short period of time (8-12 weeks) as with licensed stop smoking medications like NRT (nicotine replacement therapy) or varenicline (Champix). For other ex-smokers their use of e-cigarettes is indefinite and allows them to continue to use nicotine in a significantly safer way than smoking (see Harm reduction section below).

Temporary abstinence
Even short periods of abstinence from smoking (1-2 hours) can result in smokers experiencing nicotine withdrawal symptoms (e.g. irritability, poor concentration and strong urges to smoke). Some smokers use e-cigarettes to help reduce these symptoms at times when they are unable to smoke cigarettes.

Harm reduction
For smokers who are unable or unwilling to stop smoking cigarettes completely, e-cigarettes offer a way of continuing smoking but at lower levels, and thereby possibly reducing the harm caused.