Electronic cigarettes are battery-powered devices that heat a liquid into an aerosol you inhale, delivering nicotine without burning tobacco. They go by many names: e-cigarettes, vapes, vape pens, pod systems. As of 2023, about 6.5% of U.S. adults use them, up from 4.5% in 2019.
How They Work
Every e-cigarette, regardless of shape or brand, has the same core components: a rechargeable lithium-ion battery, a small heating coil wrapped around a wick, and a reservoir of liquid. The battery sends current through the coil, which heats up and vaporizes the liquid that the wick draws toward it. You inhale the resulting aerosol through a mouthpiece. There’s no flame, no ash, and no combustion.
Coil temperatures vary widely depending on the device, power settings, and how long you draw on it. Under normal conditions with a properly saturated wick, temperatures typically range from about 145°C to 334°C. If the wick dries out, temperatures can spike above 1,000°C, producing a harsh, unpleasant hit and significantly more toxic byproducts.
What’s in the Liquid
E-liquid has four basic ingredients: propylene glycol, vegetable glycerin, nicotine, and flavorings. Propylene glycol and vegetable glycerin are the bulk of the mixture, typically blended in ratios like 70/30 or 50/50. Propylene glycol carries flavor more effectively and produces a stronger throat sensation, while vegetable glycerin is thicker and creates denser vapor clouds. Nicotine and flavoring compounds make up the remainder.
Nicotine concentrations vary enormously. Older-style devices often used liquids in the 3 to 12 mg/mL range. Newer pod-based systems popularized nicotine salt formulations at much higher concentrations, sometimes 50 mg/mL or more. Nicotine salts have a lower pH than traditional freebase nicotine, which makes them smoother to inhale at high concentrations and allows the devices to deliver nicotine more efficiently per puff.
Types of Devices
E-cigarettes have gone through several generations, each with distinct characteristics.
First-generation devices, called “cigalikes,” look like traditional cigarettes. They’re small, low-powered, use prefilled cartridges, and are often fully disposable. Their nicotine delivery is the weakest of any type.
Second-generation devices resemble pens or small tubes. They have rechargeable batteries, refillable tanks (sometimes called clearomizers), and deliver more nicotine than cigalikes. These are what most people picture when they hear “vape pen.”
Third-generation devices, known as “mods” or “box mods,” are larger and let users adjust wattage and voltage. They use refillable tanks and rebuildable atomizers, appealing to hobbyists who want to customize their experience. Nicotine delivery is generally the highest among these first three generations.
Fourth-generation devices are pod systems. They’re compact, often draw-activated (no button), and use small pods that can be prefilled or refillable. This category includes many of the most popular devices on the market today and is where nicotine salt liquids became mainstream.
How Aerosol Compares to Cigarette Smoke
E-cigarette aerosol is chemically much simpler than cigarette smoke. Cigarette smoke contains over 6,500 identified compounds. Flavored e-cigarette aerosol contains roughly 94 to 139 compounds, and unflavored aerosol contains fewer still. By weight, 89 to 99% of e-cigarette aerosol is just glycerin, propylene glycol, water, and nicotine. In cigarette smoke, 58 to 76% of the particulate matter is made up of minor chemical constituents.
Targeted toxicants in e-cigarette aerosol run 88 to over 99% lower than in cigarette smoke under intensive puffing conditions. Tobacco-specific nitrosamines, a major class of carcinogens in cigarettes, were undetectable in e-cigarette aerosol. Carbon monoxide, benzene, 1,3-butadiene, and hydrogen cyanide were either absent or undetectable in the e-cigarette samples tested. None of the phenolic toxicants measured in cigarette smoke were found in e-cigarette aerosol at quantifiable levels.
That said, “much lower” is not the same as zero. E-cigarette aerosol can still contain cancer-causing chemicals and ultrafine particles that penetrate deep into lung tissue. Research has shown that even at relatively low coil temperatures, below 200°C, propylene glycol and glycerin can break down in the presence of oxygen to produce formaldehyde, acetaldehyde, and formic acid. The flavoring chemical diacetyl, linked to serious lung disease, has also been found in some e-liquids.
Effectiveness for Quitting Smoking
A landmark randomized trial published in the New England Journal of Medicine compared e-cigarettes to traditional nicotine replacement products like patches and gum for smoking cessation. Both groups also received behavioral support. After one year, 18% of the e-cigarette group had stayed smoke-free, compared to 9.9% in the nicotine replacement group. The e-cigarette group also reported greater reductions in coughing and phlegm production over the year.
Those numbers highlight both the promise and the limitation: e-cigarettes roughly doubled the quit rate, but more than 80% of participants in either group did not achieve sustained abstinence. Using both e-cigarettes and regular cigarettes simultaneously, known as dual use, is not an effective harm-reduction strategy. It can actually result in greater toxin exposure and worse respiratory outcomes than using either product alone.
Regulatory Status in the U.S.
The FDA regulates e-cigarettes as tobacco products, not as medical devices or cessation aids. Manufacturers must submit premarket tobacco product applications demonstrating that their products are “appropriate for the protection of public health.” As of late 2025, only 39 e-cigarettes have received FDA authorization. These are the only ones that can legally be sold in the United States.
Authorization does not mean the FDA considers these products safe or has “approved” them in the way it approves medications. It means the agency determined that, on balance, allowing them on the market is better for public health than removing them, largely because some adult smokers use them as an alternative to combustible cigarettes. Meanwhile, the vast majority of e-cigarette products on the market, particularly flavored disposables popular among younger users, remain unauthorized.
Who Uses Them
Adult e-cigarette use in the U.S. has climbed steadily, from 4.5% in 2019 to 6.5% in 2023, with a notable dip to 3.7% in 2020 during the early pandemic period. Youth use has moved in the opposite direction more recently: 5.9% of middle and high school students reported using e-cigarettes in 2024, down from 7.7% in 2023.
Nicotine at any age is addictive, but the developing brain is particularly vulnerable. Nicotine exposure during adolescence can affect memory, concentration, learning, and impulse control. During pregnancy, nicotine can damage the developing brain and lungs of a fetus. These risks apply regardless of whether the nicotine comes from a cigarette or an e-cigarette.