Electronic cigarettes are battery-powered vaporizers that simulate the feeling of smoking, but without tobacco. Their use is commonly called "vaping". Instead of cigarette smoke, the user inhales an aerosol, commonly called vapor, typically released by a heating element that atomizes a liquid solution known as e-liquid. The user activates the e-cigarette by taking a puff or pressing a button. Some look like traditional cigarettes, but they come in many variations. Most are reusable but there are also disposable versions called first-generation cigalikes; there are also second, third, and fourth-generation devices.
The benefits and the health risks of e-cigarettes are uncertain, and the long-term health effects are unknown. Compared to smoking tobacco, e-cigarettes are probably safer for both users and bystanders. There is tentative evidence that they can help people quit smoking, although they have not been proven to work better than regulated nicotine replacement products, and the regulated medication is safer. Their usefulness in tobacco harm reduction is unclear, but they could form part of future strategies to decrease tobacco related death and disease. Overall their safety risk to users is similar to that of smokeless tobacco. No serious adverse effects from e-cigarettes have been reported in trials, while less serious adverse effects include throat and mouth inflammation, vomiting, nausea, and cough. Non-smokers who use e-cigarettes risk becoming addicted to nicotine, a chemical with a range of harmful effects.
The e-liquids used in e-cigarettes usually contains a mix of propylene glycol, glycerin, nicotine, and flavorings. Some e-liquids may contain ingredients such as cannabis, tobacco extract, or adulterants. E-cigarettes create a vapor consisting of ultrafine particles whose composition varies across and within manufacturers. The vapor can contain small amounts of toxins, including traces of heavy metals detected at levels permissible in inhalation medicines, and some potentially harmful chemicals not found in tobacco smoke at levels permissible by workplace safety standards. However, chemicals may exceed the more stringent safety limits which are relevant to the population as a whole. High aldehyde levels, which have been generated in laboratory settings by researchers overheating e-liquid, cause a highly aversive acrid taste that users would not subject themselves to.
The modern e-cigarette arose from a 2003 invention by Chinese pharmacist Hon Lik, and as of 2015 most e-cigarettes were made in China. Since their introduction to the market in 2004, global usage has risen exponentially. For instance, in the UK user numbers have increased from 700,000 in 2012 to 2.6 million in 2015, In the United States e-cigarettes are used by a significant percentage of youth and adults. Most people's reason for using e-cigarettes is related to trying to quit smoking, though many people use them recreationally. A majority of e-cigarette users still smoke traditional cigarettes, leading to concerns that dual use can "delay or deter quitting". About 60% of UK users are smokers and about 40% are ex-smokers, while use among never-smokers remains "negligible". Because of the potential relationship with tobacco laws and medical drug policies, e-cigarette legislation is being debated in many countries. The European Parliament passed regulations in February 2014, to come into effect by 2016, standardizing liquids and personal vaporizers, listing ingredients, and child-proofing liquid containers. The US FDA published proposed regulations in April 2014 with some similar measures. As of 2014, there were 466 brands of e-cigarette with sales of around $7 billion.