The electronic cigarette was invented in the mid 20th century. There are two patents for electrical smoking devices that are substantially similar to today's e-cigarette, which were never manufactured in quantity, and lapsed. Later, in China in the late 90's, Han Li (alt. spelling: Hon Lik), a chemist and engineer who had seen his father die of cancer, invented the modern version with electronic battery controls, and patented it in 2003.
As a smoker himself, he wanted to find a way to obtain nicotine but without the risk to health, and believed that if the smoke could be removed, then so would most of the risk. The idea was simply to continue to 'smoke' - but without the smoke. He formed a company called Ruyan (Rú yān ( 如烟 - which in translation can best be said to mean "Like Smoke") to market his invention. The company was absorbed by Dragonite, who now own Han Li's patents.
Introduced in the UK in 2005, by early 2006 e-cigarettes were more widely available, and were introduced in the USA by the end of the year. It is thought that by 2007 there were about 1,000 e-cigarette owners in the UK, and the world's first internet forum on the topic was started in London at the end of 2007 (ECF). The averaged growth in use of e-cigarettes was about 500% per year to Q2 2011 in the UK, with about 300,000 owners there by that time, the UK market being worth over £10m then.
Growth at Q2 2012 was between 40% and 100% per year in the UK depending on the metric in question (user numbers or units sold or gross market value). By Q1 2013 there were between 600,000 (lowest estimate) and 800,000 (extrapolation of the ASH UK's Q2 2012 figure of 650,000) UK e-cigarette owners, and the market was worth over £50m annually. Between 6% and 7% of UK smokers had switched to e-cigarettes by early 2013. There will be more than 1 million ecig users in the UK by the end of 2013 and possibly earlier at Q3.
Growth in the US has been much stronger - phenomenal, in fact - as there are now about 3 million current users, with the market worth $250m or more at Q2 2012, from scratch at late 2006. The original forum can now have 3,000 people online at one time, around 12,000 posts per day, over 300,000 posts per month, and over 8 million pages on the sitemap (Q1 2013). Electronic cigarettes are proving not just popular - use is increasing at a stunning rate.
What is an e-cigarette ?
A standard electronic cigarette, also known as a 'mini', has either two or three parts: a battery, atomizer and cartridge; or a battery and combined atomizer-cartridge.
The battery is normally a 3.7 volt rechargeable Li-ion cell, with some electronics packaged with it to control the recharge and discharge state.
The atomizer is a tiny coil of nichrome wire that heats the liquid and vaporises it. A simplified description of how it works is that it is a combination of a toaster and a kettle: the heater coil is exactly the same as that in a toaster but on a smaller scale; and in use it works like a kettle, as the coil heats up while immersed in a liquid bath. The result looks like steam as it is a mist, and utilises the same ingredient used in disco fog machines to create visible vapor - it is a low-temperature water-based vapor . The designed purpose is to replicate smoking as closely as possible, so there are some functional differences between an e-cigarette and a medical nicotine inhaler.
The cartridge contains the refill liquid, which is normally held in some sort of sponge or foam, and gravity-feeds it to the heater element.
Larger models with improved performance are now available. The benchmark model is no longer the Mini, but the Mid-Size models that resemble a cigar in size (such as the eGo), with larger batteries for improved performance in both vapour output and battery charge life.
Specialist models known as APVs (advanced personal vapourisers) are also available, with advanced functions such as digital readouts, variable power, and XL batteries.
Technical advances from the early days mean that there are now three distinct classes of e-cigarette (the Mini, Mid-Size and APV), and the benchmark model is now the Mid-Size, eGo-type of ecig. There is approximately a 100% performance increase in each step up in the model range.
The Minis serve as introductory models for new vapers and for those who were light or occasional smokers. 92% of vapers polled at a typical large-scale meet had upgraded from their Mini to a more efficient model.
What is in the liquid ?
There are usually less than 10 ingredients in the liquid refill or e-liquid as it is often termed, and this compares favourably with the 5,300-plus identified in the latest research on cigarette smoke. Some brands may have only 4 ingredients, some as many as 20; all ingredients are considered innocuous since all except some flavours have many years of safe use for inhalation. In some cases there are 70 years of safe inhalation use of these materials.
The vapour is composed of, in order of ingredient percentage: water vapour, flavouring, visibility component, and nicotine.
There are various recipes for liquid that are proprietary to each manufacturer; some are marketed as of the simplest possible make up, some for their exotic flavours. The liquid normally contains PG  and/or VG , plus flavourings such as coffee or chocolate. Once users' sense of taste has returned, they tend to prefer alternative flavours over tobacco, though a combination of the two is popular.
There is no sidestream smoke from an e-cigarette, only what is exhaled by the user, which is mostly water vapour since the majority of the other materials have been absorbed.
Some owners, about 7% according to polls, use zero-nic liquid: refill liquid with flavouring but no nicotine.
What are the health issues ?
Death and disease associated with smoking are are almost exclusively caused by the smoke and products of combustion. If the smoke and combustion products such as carbon monoxide are removed, risk is considerably reduced, probably by at least 98% even for consumption of a whole-tobacco product.
With smokeless tobacco products (i.e. oral tobacco), if the carcinogens introduced by the tobacco curing process are also removed by special processing, as is carried out with Swedish Snus, the risk becomes so low that it cannot be reliably identified by statistical methods - decades of statistical epidemiology from Sweden cannot reliably identify any elevation of risk for consuming a smokeless tobacco product that has been processed to remove most of the carcinogens. If nicotine alone is consumed, the risk is unmeasurably low.
Nicotine Nicotine is not a significantly harmful material, it is of course a normal and natural part of the diet and everyone tests positive for it (it is a normal ingredient in many vegetables, tea, and so on). A reasonable increase of the dietary supply of nicotine most likely has the same risk profile as coffee / caffeine consumption. Nicotine cannot cause cancer or any of the other diseases caused by smoking, as it is the smoke that does this.
"It is impossible for e-cigarettes to cause lung cancer" - Dr M Laugesen.
"Nicotine consumption has about as much implication for health as consuming coffee or fries" - Prof C Phillips.
Because of the national health statistics and the huge volume of research data on Snus consumption from Sweden, it is also known that nicotine does not promote cancer in any way.
People who say that nicotine is a dangerous, toxic chemical presumably know little or nothing about nutrition: nicotine is part of the diet; everyone everywhere tests positive for it; and it is co-located in the same plants as nicotinic acid, which you may know better as Vitamin B3 or niacin (which can also be a metabolyte of nicotine). Like similar materials it is normally only present in very small quantities; boosting the normal dietary amounts by about 5 - 10 times, as smokers do, has no discernible effect on health at population level as long as the nicotine is delivered without smoke. This is proven by the Swedish health statistics.
With the smoke removed, a user's risk drops by several orders of magnitude. E-cigarettes are extremely unlikely to cause cancer, heart disease, arterial disease, or COPD as there is nothing in the vapor that can cause this. There is no smoke.
Carcinogens are only present at trace levels of circa 8ng/mg, exactly the same as in NRTs such as nicotine skin patches, for example. These levels according to Prof Rodu are, "A million times lower than conceivably harmful to health".
Research This is why all the extensive research on e-cigarettes, and all the senior medical figures who have carried out this research or inspected it and commented on it, reinforce the fact that e-cigarettes are already known to be far safer than tobacco cigarettes, and that they should be introduced as swiftly as possible as an alternative to smoking, since millions of lives will be saved if this is done. Prof Britton of the RCP, for example, tells us that if all UK smokers switched to e-cigarettes, five million lives would be saved, just of those who are currenly alive today.
The huge importance of this to public health cannot be overestimated; indeed, it is probably correct to say that this is the most important development since the discovery of antibiotics.
There is a long list of senior medical figures such as professors in charge of public health programmes in universities, doctors who are clinical researchers, and organisations such as the AAPHP, the American Association of Public Health Physicians, and the ACSH, the American Council for Science and Health, who have examined the evidence and pronounced e-cigarettes as safe for use as an alternative smoking method with the object of saving lives.
You can find the published work of many world authorities on tobacco and public health, both in the medical literature or on the internet, and these authorities overwhelmingly support the introduction of e-cigarettes as a population-level method to reduce smoking disease and death, as has been achieved in Sweden already by the use of their specially-processed local smokeless tobacco.
For example: Prof B Rodu - the leading authority on the oral pathology of tobacco consumption; Prof C Phillips - the leading authority on the science basis and epidemiology of Tobacco Harm Reduction; Dr J Nitzkin - Chair, Tobacco Control Task Force, AAPHP, American Association of Public Health Physicians; Prof M Siegel - the first world-renowned scientist and expert on tobacco and health to fully support e-cigarettes; Prof G Stimson - world-renowned public health expert, and 40-year veteran of Harm Reduction and one of its principal architects; Prof R Polosa - pulmonologist and authority on broncho-provocation (airway challenge) and tobacco; Dr M Laugesen - the first clinical researcher to evaluate e-cigarettes scientifically; Prof C Bullen - world-renowned clinical research director; Prof J Britton - Chair of the Tobacco Group of the Royal College of Physicians (RCP).
And we should also mention the world's most prominent campaigners against smoking harm, who also fully support a move to e-cigarettes: Bill Godshall - Director of Smokefree Pennsylvania, recognised as the world's most committed and successful anti-smoking harm campaigner; Clive Bates - ex-Director of ASH UK and an expert on smoking harm issues; Prof D Sweanor JD - senior law adviser and expert on smoking harm issues to a multitude of organisations including the W.H.O., World Bank; he has received various awards for his work including a ‘Public Health Hero’ lifetime achievement award; Scott Ballin - anti-smoking harm advocate, held senior positions with the American Heart Association and Chair of the Coalition on Smoking or Health (ASC, ALA, AHA).
There is absolutely no way these senior public health authorities and campaigners would place their support behind e-cigarettes unless the issues were very clear-cut.
Knowledge base It is important to note that a great deal of research has been carried out on e-cigarettes. As an example, we know much more about what is in them than we do about what is in cigarette smoke. Any statements that contradict this are untrue, and most likely some form of propaganda. E-cigarettes have been used by millions of people, globally, for many years, and there are no incidents of mortality or significant morbidity that can be directly linked to e-cigarette use. As yet there is no long-term population data but this will not be available for another two decades.
It should also be carefully noted that even when this is available, as is the case for Snus - proven safe by three decades of research and the hundreds of clinical studies that say so, and by the simple fact that Sweden reduced their smoking prevalence by 45% with a concomitant fall in the smoking-related death rate to a uniquely low level - it will not stop the propaganda and lies about the products. There are many powerful interests with a huge investment in protecting the status quo and maintaining smoking at current levels: the tobacco industry, the pharmaceutical industry, and tax departments. All will lose a fortune if Tobacco Harm Reduction products become widely available - cigarette sales plunge, smoking-related disease and death rates fall through the floor, pharmaceutical sales for treating sick smokers collapse. It already happened in Sweden, so there is no tenable argument about this.
Individual health issues It is certainly true that some users will be intolerant to some ingredients. The effects of such intolerance can be reduced or eliminated by changing to a different brand of e-liquid with a different ingredient profile. There is such a wide range of base materials, types and flavours available that it is impossible for all users to be completely tolerant to all materials. As time progresses, we will have a better understanding of the multitude of minor issues that present. All we know at present is that if e-cigarette use replaces smoking for significant numbers of smokers, as seems possible given time and support, then smoking disease rates are likely to fall by a similar or identical amount, as no disease vectors can be shown for e-cigarette use.
What is the legal situation ?
Electronic cigarettes are legal to import, own and use in the UK, US, and most European countries. There had been opposition to them by individual government agencies in both the UK and US, but these objections were quashed by the courts (in the US) and higher government (in the UK). It was claimed that "there was little research", or "we don't know what's in them", or "we don't know much about them" - but since such statements are outright lies, and since there was a long list of professors, doctors and epidemiologists who could refute those statements, and due to the fact that after extensive use by millions of people there has been no report of harm, the actions to ban e-cigarettes were overturned. In fact e-cigarettes can now be shown to be thousands of times safer than quit-smoking drugs such as Chantix .
After many years of use by millions of people all around the world, there is not one single incident of death or disease attributed to e-cigarette use.
Why is there opposition to them ?
It's quite simple: some people will lose a fortune if e-cigarettes become popular. Despite the fact that anyone can see that widespread use of e-cigarettes will certainly save hundreds of thousands of lives, priority is being given to maintaining current income streams over the saving of life.
The biggest loser will be the pharmaceutical industry, as their extremely profitable drug treatments for sick and dying smokers will be savagely cut. This is a $100bn annual market, and one that may shrink by 60% if the expected mass shift to ecigs eventually takes place. The far smaller NRT and smoking cessation phramacotherapy market (about $3bn annually) will also take the same hit, since if there is a safe alternative to smoking, preferred by millions of people (as is the case now, with e-cigarettes), then why quit smoking? Why buy drugs that cost the same or more than smoking? Why take drugs with a substantial risk, such as Chantix ? Why buy drugs that cost even more than smoking (like the Nicotrol inhaler)? Why buy drugs that are almost guaranteed to fail ?
They are desperate to avoid this and are fighting hard to have e-cigarettes banned or restricted - and with some success, as they have millions of dollars available for this purpose .
The Tobacco Control industry will also be big losers since their pharma funding will diminish, and their work become less and less relevant. As a result, they are fighting a strong rearguard action against alternative products with a greatly-reduced risk.
Wherever you see opposition to e-cigarettes you will find pharma funding. Why else would anyone object to something that will save millions of lives ?
What does the future hold ?
At some stage, 25% of smokers will be using an e-cigarette. We don't know when this will be but it is not that far off - perhaps by 2025, perhaps earlier. Certainly, at early 2013 we know that 6% of smokers have switched. If the current rate of growth continues then the 25% mark will be reached even sooner and perhaps by 2020.
Keep in mind that Sweden reduced the number of smokers by 45%, by allowing free and unhindered purchase of smokeless tobacco (Snus). The death rate dropped in parallel, which is why they have the lowest smoking-related death rate of any developed country by a wide margin. As e-cigarettes are more popular with smokers, it is reasonable to believe that ecigs will outperform Snus both in smoker conversions and in the number of lives saved as a result.
It is expected that the pharmaceutical industry will succeed in having e-cigarettes banned in some countries, and restricted in others where they do not succeed in obtaining a ban. They will be aided by the pharmaceutical licensing aulthorities in each country, as those agencies in practice act as the legal arm of the pharma industry - they never take any action that would severely impact pharma income, and where possible they assist in removing commercial competitors. As examples, note their success in having Snus banned throughout Europe at the cost of tens of thousands of lives , and the recent ban on herbal medicines by the enforcement of completely unwarranted medical licensing in order to restrict sales of products with a 30-year safe usage history that competed with pharmaceutical products.
As a result, some (or many) e-cigarette users will have resort to black market supplies of e-cigarettes and materials in order to exercise their right of choice and their right to life. This may be a historic event when it occurs, as it might be the first time that people have had to go to the black market for safer materials in order to stay alive, in contrast to the more usual practice of obtaining dangerous substances.
It will also be most people's first real taste of government corruption and its direct effect on them.
 The visibility and vapour-body ingredient PG, propylene glycol, is also used in asthma inhalers and the nebulisers used by lung transplant patients, and has 70 years of documented research - so we know it is safe.
 VG, vegetable glycerine, is a popular food additive and skin care ingredient. It is also used in inhalable medicines; there is currently a general move among pharmaceutical manufacturers to replave PG with glycerine in inhalers, as it has less of a drying-out effect on the throat than PG. Glycerine has multiple pharmaceutical licenses for inhalation; see for example Dow Optim.
It creates more visible vapor than PG but has less TH or throat hit, the effect that replicates cigarette smoke in the throat.
 Hundreds of suicides are directly attributed to the quit-smoking drug Chantix / Varenicline. It can induce severe (but temporary) psychosis, leading to severe depression, uncontrollable rage, violence, and suicide (also one reported case of multiple murder). There are now two separate clinical trials that show it causes a cardiac event for 1 in 30 patients, and is therefore thought to have been responsible for over 60,000 cardiac incidents, just in the USA, just in 2010. The FDA now admits to 272 deaths attributable to Chantix (Q1 2013), although some commentators say this figure is likely to be three or four times higher in reality.
 The success rate for pharmaceutical interventions for smoking cessation is, on average, 1 in 10. Independent research shows that NRTs taken without being part of a mentoring program have a success rate much lower, of about 2%. Mentored programs can improve this success rate to around 7%; but the fact remains that the vast majority of people - from about 90% to 98% - taking these medicines will fail to quit smoking, and everybody knows that most will fail. The averaged failure rate of patients using pharmaceutical interventions to quit smoking is about 95%. There are some drugs with a slightly higher success rate, such as Chantix, but these are high-risk choices now rendered unattractive by much safer and effective alternatives such as e-cigarettes.
 In 2009 the pharmaceutical industry had more lobbyists in Washington, USA than there were Congressmen. They declared a $264 million spend on lobbying in that year. The same resources are available in any country that needs their attention - and those countries will be where smoking illness treatment drug sales are high, such as the UK.
 Anecdotal evidence shows a success rate of 75% is common when assisting people to switch to an e-cigarette. Contrast ref#4 with this. We estimate that a mentored program based around e-cigarettes and Snus would have a success rate so high that it would eclipse all previous programmes of any kind - leading to about a 60% overall success rate in time.
A reduction of 45% in the smoking-related death rate has been suggested as probable for a country where Snus is widely promoted (as this is the case in Sweden), and the likely result for e-cigarettes would be better than this. If both were freely available and widely promoted, it is not unreasonable to assume the death rate would drop by the same amount as the expected percentage switch by smokers to THR products: about 59% - 60%.
 Snus, a Swedish oral tobacco that is specially processed to remove carcinogens, is the best proven alternative to smoking, and the most successful Tobacco Harm Reduction product. There are 30 years of research in Sweden that show Snus users have the same risk as non-smokers, and that as a consequence it is a far safer alternative to smoking. For example a Snus user has not only the same risk of contracting lung cancer as a non-smoker, but also the same risk for oral cancer. Despite this, Snus is banned throughout the rest of Europe, as it would damage cigarette sales, pharmaceutical sales for smoking illness treatment drugs, NRT sales, and tobacco tax revenues.
Snus would eventually reduce smoking-related sickness by 44% to 45%; and the effect on the vast and immensely-profitable drug treatment market for sick smokers would be catastrophic. E-Cigarettes are thought to have an even higher potential, which is why resistance to them is strong.