flavor, often using blends that mimic popular cannabis strains or sugary foods such as candy or cereal. While vape pens deliver higher concentrations of THC to cannabis users, the psychoactive effects are reported to be shorter lasting than the effects of vaporizing or smoking traditional marijuana. Of the studies that have investigated cannabis vaporization, few have addressed the quality of the vapor extracted and delivered; instead, studies usually focus on the mode of usage of the vaporizers. However, those that have addressed vapor quality have demonstrated promising results. Such studies suggest that the absence of combustion results in an aerosol that contains significantly lower amounts of harmful substances found in smoke, such as tar, carbon monoxide, and carcinogenic compounds known as polynuclear aromatic hydrocarbons (PAH). One study found that cannabis smoke contains 111 compounds (including several carcinogenic PAHs) in addition to the cannabinoids, whereas only 3 additional compounds were identified in cannabis vapor, other than the cannabinoids. This suggests that the vaporization of cannabis may be a safer alternative to combusted cannabis. E-cigarette vaporizers An electronic cigarette 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 combusting tobacco. Using an e-cigarette is known as "vaping" and the user is referred to as a "vaper." Instead of cigarette smoke, the user inhales an aerosol, commonly called vapor. E-cigarettes typically have a heating element that atomizes a liquid solution called e-liquid. E-cigarettes may be automatically activated by taking a puff; others turn on manually by pressing a button. Some e-cigarettes look like traditional cigarettes, but they come in many variations. Most versions are reusable, though some are disposable. There are first-generation, second-generation, third-generation, and fourth-generation devices. E-liquids usually contain propylene glycol, glycerin, nicotine, flavorings, additives, and differing amounts of contaminants. E-liquids are also sold without propylene glycol, nicotine, or flavors. The benefits and the health risks of e-cigarettes are uncertain. There is tentative evidence they may help people quit smoking, although they have not been proven to be more effective than smoking cessation medicine. There is concern with the possibility that non-smokers and children may start nicotine use with e-cigarettes at a rate higher than anticipated than if they were never created. Following the possibility of nicotine addiction from e-cigarette use, there is concern children may start smoking cigarettes. Youth who use e-cigarettes are more likely