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It can be hard to know quite what to make of e-cigarettes.

Last week the World Health Organization called for a ban on their use in public places and workplaces. The group said it was concerned about the risk which use of the products presented and about their marketing via fruit and candy-style flavours.

Highly-respected bodies in the UK such as the British Medical Association and Faculty of Public Health have also sounded notes of caution.

But there is also a vociferous health lobby warning against over-regulation, arguing that getting smokers to switch to e-cigarettes could actually save lives.

Confused? You won't be the only one.

The arguments raging over the role and risks of e-cigarettes are typical of many that have been heard down the years in the field of health. That is to say it is all about balancing risk and benefit - and as evidence is still emerging it is natural to find a variety of opinion.

After all, e-cigarettes are a relatively new phenomenon. Since 2005, the e-cigarette industry has grown from one manufacturer in China to an estimated £1.8bn global business with 466 brands.

And it is worth noting, because of the unease it is causing health experts, it's an industry that tobacco firms are increasingly getting involved in.

But this debate is further complicated by the fact that it is not just the merits of e-cigarettes that is being discussed, but their impact on smoking tobacco products.

On their own, there is little to recommend the use of e-cigarettes. They contain some toxins and, therefore, in theory are potentially harmful.

But, of course, that cannot be seen in isolation. Smoking an e-cigarette - and this is about the only thing that is not disputed - is less harmful than tobacco products. Much less harmful, in fact.

This - according to those who are worried about the tough line being taken by some experts - should be the guiding principle while more research is carried out.

1. On some e-cigarettes, inhalation activates the battery-powered atomiser. Other types are manually switched on

2. A heating coil inside the atomiser heats liquid nicotine contained in a cartridge

3. Liquid nicotine becomes vapour and is inhaled. The 'smoke' produced is largely water vapour. Many e-cigarettes have an LED light as a cosmetic feature to simulate traditional cigarette glow.

But the problem for those who have been more circumspect is that there are a number of unknowns.

The major concerns about e-cigarettes is that they could act as a gateway to real cigarettes. The experts who are in the news today make a pretty strong case for that not being the case. But plenty of people are still not convinced.

However, there are other questions that need to be answered too.

Research has shown that while e-cigarettes can increase the chances of quitting, they are less effective than traditional "stop smoking" services.

If the availability of e-cigarettes is stopping people using official routes to quitting - and there is some evidence to suggest they may be - that could be a concern.

Another worry is that people who use e-cigarettes to quit could be more likely to relapse.

Meanwhile - and this is a point acknowledged by Prof Robert West who is one of the experts warning against an over-reaction to e-cigarettes - the presence of people "vaping" may encourage those who have quit successfully to take up the habit.

These are the sort of issues that are now being looked into by researchers across the world. While that is happening, it's a debate that still has a long way to run.