An electronic cigarette is an electronic device that simulates tobacco smoking. It consists of an atomizer, a power source such as a battery, and a container such as a cartridge or tank. Instead of smoke, the user inhales vapor. As such, using an e-cigarette is often called "vaping". The atomizer is a heating element that atomizes a liquid solution called e-liquid. E-cigarettes are activated by taking a puff or pressing a button. Some look like traditional cigarettes, and most versions are reusable.E-cigarettes create an aerosol, commonly called vapor, made of particulate matter. The vapor typically contains propylene glycol, glycerin, nicotine, flavors, and traces of nitrosamines, other toxicants, carcinogens, heavy metals, and metal nanoparticles. Its exact composition varies, and depends on several factors including user behavior.The health effects of electronic cigarettes remain uncertain, but they are likely less harmful than smoking tobacco. E-cigarette vapor contains fewer toxic chemicals, in lower concentrations, than cigarette smoke, but also contains harmful chemicals not found in tobacco smoke.Nicotine is highly addictive, and can be toxic at high levels, although poisoning is almost impossible when products are used as directed; however, accidental ingestion can be fatal. People who vape are more likely to start smoking. For smokers who are unable or unwilling to quit using conventional smoking cessation methods such as nicotine replacement therapy (NRT), vaping has a role in tobacco harm reduction.