An electronic cigarette or e-cigarette[notes 1] is a handheld battery-powered vaporizer that simulates smoking by providing some of the behavioral aspects of smoking, including the hand-to-mouth action of smoking, but without burning tobacco.[68] Using an e-cigarette is known as "vaping" and the user is referred to as a "vaper."[2] Instead of cigarette smoke, the user inhales an aerosol, commonly called vapor.[69] E-cigarettes typically have a heating element that atomizes a liquid solution called e-liquid.[4] The user automatically activates the e-cigarette by taking a puff;[5] other devices turn on manually by pressing a button.[2] Some e-cigarettes look like traditional cigarettes,[6] but they come in many variations.[2] Most versions are reusable, though some are disposable.[7] There are first-generation,[8] second-generation,[9] third-generation,[10] and fourth-generation devices.[11] E-liquids usually contain propylene glycol, glycerin, nicotine, flavorings, additives, and differing amounts of contaminants.[12] E-liquids are also sold without propylene glycol,[13] nicotine,[14] or flavors.[80]