An electronic cigarette (e-cig or e-cigarette), personal vaporizer (PV) or electronic nicotine delivery system (ENDS) is a battery-powered vaporizer which has a similar feel to tobacco smoking. Electronic cigarettes do not contain tobacco, although they do use nicotine from tobacco plants. They do not produce cigarette smoke but rather an aerosol, which is frequently but inaccurately referred to as vapor. In general, they have a heating element that atomizes a liquid solution known as e-liquid. E-liquids are usually a mixture of propylene glycol, glycerin, nicotine, and flavorings. Others have similar ingredients but without nicotine. The benefits and risks of electronic cigarette use are uncertain. One review found evidence of a benefit as a smoking cessation aid from a small number of studies. Another considered the data to be inconclusive. Their role in tobacco harm reduction as a substitute for tobacco products is unclear. They appear to be similar in safety to other nicotine replacement products, but there is not enough data to draw conclusions. The evidence suggests that the US Food and Drug Administration (FDA) accepted products such as a nicotine inhaler may be a safer way to give nicotine than e-cigarettes. The limited evidence suggests that e-cigarettes are safer than traditional cigarettes. Electronic cigarettes may carry a risk of addiction in those who do not already smoke, but there is no evidence of ongoing use among those who have never smoked. They may promote delaying of quitting smoking, or act as a deterrent to quitting. Emissions from e-cigarette may contain tiny ultrafine particles of flavors, aroma transporters, glycerol, propylene glycol, nicotine, tiny amounts of carcinogens and heavy metals, and other chemicals. The evidence indicates the levels of contaminants do not warrant health concerns according to workplace safety standards. E-cigarette emissions have fewer toxic components than cigarette smoke. They are likely to be less harmful to users and bystanders. No serious adverse effects from e-cigarette have been reported in trials. Less serious adverse effects from e-cigarette use include throat and mouth inflammation, vomiting, nausea, and cough. The frequency of use has increased with up to 10% of American high school students having ever used them as of 2012 and around 3.4% of American adults as of 2011. In the UK the number of e-cigarette users has increased from 700,000 in 2012 to 2.1 million in 2013. About 60% are smokers and most of the rest are ex-smokers. E-cigarette users most commonly continue to smoke traditional cigarettes. Current e-cigarettes arose from an invention made by Hon Lik in China in 2003, and devices are mostly manufactured in China. E-cigarette brands have increased advertising with similar marketing to that used to sell cigarettes in the 1950s and 1960s. Because of the possible relationship to tobacco laws and medical drug policies, electronic cigarette legislation is being debated in many countries. The European Parliament passed regulations in February 2014 requiring standardization of liquids and personal vaporizers, listing of ingredients, and child-proofing of liquid containers. The US Food and Drug Administration (FDA) published proposed regulations in April 2014 with some similar measures.