'Smokless' smokes for smokers

An electronic cigarette (e-cig or e-cigarette), personal vaporizer (PV) or electronic nicotine delivery system (ENDS) is a battery-powered vaporizer which simulates tobacco smoking by producing an aerosol that resembles smoke.

E-liquids usually contain a mixture of propylene glycol, vegetable glycerin, nicotine, and flavorings, while others release a flavored vapor without nicotine.
The benefits and risks of electronic cigarette use are uncertain.
Safety
The risks of electronic cigarette use are uncertain. This is due to there being little data regarding their health effects and to the variability of vaporizers and variability in liquid ingredients and in their concentration and quality, and thus variability of the contents of aerosol delivered to the user. However, some evidence suggests e-cigarettes may be safer than smoking tobacco products, and possibly as safe as other nicotine replacement products but there is insufficient data to draw conclusions. Switching from smoking tobacco to using e-cigarettes may result in reduced exposure to nicotine and reduced potential risk of disease from smoking.

A preliminary analysis of e-cigarette cartridges by the US Food and Drug Administration (FDA) in 2009 identified that some contain tobacco-specific nitrosamines (TSNAs), known cancer-causing agents. The amounts of TSNAs present were on par with existing NRT products like nicotine gum and inhalers. The FDA's analysis also detected diethylene glycol, a poisonous and hygroscopic liquid, in a single cartridge manufactured by Smoking Everywhere and nicotine in one cartridge claimed to be nicotine-free. Diethylene glycol was found in a cartridge tested in 2009 by the FDA, but in 2011 researchers reviewed the data and noted that 15 other studies had failed to find any evidence of this chemical in e-cigarettes. Further concerns were raised over inconsistent amounts of nicotine delivered when drawing on the device. In some e-cigarettes, "Tobacco-specific impurities suspected of being harmful to humans – anabasine, myosmine, and β-nicotyrine – were detected in a majority of the samples tested." The UK National Health Service noted that the toxic chemicals found by the FDA were at levels one-thousandth that of cigarette smoke, and that while there is no certainty that these small traces are harmless, initial test results are reassuring. While propylene glycol and other chemicals commonly used as solvents or carrier compounds in c-cigarettes liquids are generally recognized as safe, they have not been used before in vaporized form over long periods of time. The risks, especially to the lungs, are not understood and are of concern to public health authorities and some reviewers.Some reviewers have noted that while there is variability in the ingredients and concentrations of ingredients in e-cigarette liquids, tobacco smoke contains thousands of chemicals, most of which are not understood and many of which are known to harmful.
Major injuries and illness have occurred from using e-cigarettes such as explosions and fires. Less serious adverse events included throat and mouth inflammation, cough, nausea, and vomiting. Liquids used with e-cigarettes also pose a risk if they are ingested or if the skin is exposed to them, especially for children. In the US, the number of cases of accidental nicotine poisoning associated with e-cigarette liquid rose from one per month in September 2010 to 215 per month in February 2014, and of calls to poison centers involving e-cigarettes and conventional cigarettes, the proportion related to e-cigarettes jumped from 0.3 percent in September 2010 to 41.7 percent in February 2014. More than half (51.1 percent) of the calls to poison centers due to e-cigarettes involved children under 5 years old.
It generally uses a heating element known as an atomizer, that vaporizes a liquid solution known as e-liquid.