An electronic cigarette is a handheld battery-powered vaporizer that simulates smoking, but without tobacco combustion. E-cigarette components include a mouthpiece (drip tip[2]), a cartridge (liquid storage area), a heating element/atomizer, a microprocessor, a battery, and some of them have an LED light on the end.[3] An exception to this are mechanical e-cigarettes (mods) which contain no electronics and the circuit is closed by using a mechanical action switch.[4] An atomizer consists of a small heating element, or coil, that vaporizes e-liquid and a wicking material that draws liquid onto the coil.[5] When the user inhales a flow sensor activates the heating element that atomizes the liquid solution;[6] most devices are manually activated by a push-button.[7] The e-liquid reaches a temperature of roughly 100–250 °C (212–482 °F) within a chamber to create an aerosolized vapor.[8] The user inhales an aerosol, which is commonly but inaccurately called vapor, rather than cigarette smoke.[9] Vaping is different than smoking, but there are some similarities, including the hand-to-mouth action of smoking and a vapor that looks like cigarette smoke.[1] The aerosol provides a flavor and feel similar to tobacco smoking.[1] A traditional cigarette is smooth and light but an e-cigarette is rigid, cold and slightly heavier.[1] There is a learning curve to use e-cigarettes properly.[10] E-cigarettes are cigarette-shaped,[11] and there are many other variations.[12] E-cigarettes that resemble pens or USB memory sticks are also sold that may be used unobtrusively.

There are three main types of e-cigarettes: cigalikes, looking like cigarettes; eGos, bigger than cigalikes with refillable liquid tanks; and mods, assembled from basic parts or by altering existing products.[14] Cigalikes are either disposable or come with rechargeable batteries and replaceable nicotine cartridges.[15] A cigalike e-cigarette contains a cartomizer, which is connected to a battery.[16] A "cartomizer" (a portmanteau of cartridge and atomizer[17]) or "carto" consists of an atomizer surrounded by a liquid-soaked poly-foam that acts as an e-liquid holder.[5] Clearomizers or "clearos", not unlike cartotanks, use a clear tank in which an atomizer is inserted.[18] A rebuildable atomizer or an RBA is an atomizer that allows the user to assemble or "build" the wick and coil themselves instead of replacing them with off-the-shelf atomizer "heads".[19] The power source is the biggest component of an e-cigarette,[20] which is frequently a rechargeable lithium-ion battery.[12]

As the e-cigarette industry continues to evolve, new products are quickly developed and brought to market.[21] First-generation e-cigarettes tend to look like traditional cigarettes and so are called "cigalikes".[19] Most cigalikes look like cigarettes but there is some variation in size.[16] Second-generation devices are larger overall and look less like traditional cigarettes.[22] Third-generation devices include mechanical mods and variable voltage devices.[19] The fourth-generation includes sub ohm tanks and temperature control devices.[23] The voltage for first-generation e-cigarettes is about 3.7[24] and second-generation e-cigarettes can be adjusted from 3 V to 6 V,[25] while more recent devices can go up to 8 V.[24] The latest generation of e-cigarettes are pod mods,[26] which provide higher levels of nicotine than regular e-cigarettes[27] through the production of aerosolized protonated nicotine.[28]

E-liquid is the mixture used in vapor products such as e-cigarettes[29] and usually contain propylene glycol, glycerin, nicotine, flavorings, additives, and differing amounts of contaminants.[30] E-liquid formulations greatly vary due to fast growth and changes in manufacturing designs of e-cigarettes.[16] The composition of the e-liquid for additives such as nicotine and flavors vary across and within brands.[31] The liquid typically consists of a combined total of 95% propylene glycol and glycerin, and the remaining 5% being flavorings, nicotine, and other additives.[32] There are e-liquids sold without propylene glycol,[33] nicotine,[34] or flavors.[35] The flavorings may be natural, artificial,[31] or organic.[36] Over 80 chemicals such as formaldehyde and metallic nanoparticles have been found in the e-liquid.[37] There are many e-liquids manufacturers in the US and worldwide,[38] and more than 15,500 flavors existed in 2018.[39] Under the US Food and Drug Administration (FDA) rules, e-liquid manufacturers are required to comply with a number of manufacturing standards.[40] The revision to the EU Tobacco Products Directive has some standards for e-liquids.[41] Industry standards have been created and published by the American E-liquid Manufacturing Standards Association (AEMSA).

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