An e-cigarette works by using a small battery-powered heating coil to bring liquid to its boiling point, turning it into an inhalable aerosol. There is no combustion, no tobacco leaf, and no flame. The device is, at its core, a miniature heat-and-mass-transfer system: electricity flows through a tiny coil of wire, the wire gets hot, and the liquid surrounding it vaporizes into fine droplets you inhale.
The Four Main Components
Every e-cigarette, from a slim disposable pen to a box-shaped mod, contains the same basic parts: a battery, a coil (sometimes called an atomizer), a wick, and a reservoir of liquid. The battery supplies electrical current. The coil converts that current into heat. The wick draws liquid from the reservoir to the coil’s surface. And the liquid itself provides the nicotine, flavor, and the visible cloud.
How these parts are packaged varies enormously. In a disposable vape, everything is sealed inside a single plastic shell. In a refillable device, the coil and wick sit inside a replaceable cartridge or tank, and the battery can be recharged. But the underlying process is identical.
How the Coil Turns Liquid Into Aerosol
When you activate the device, the battery sends direct current through the coil, a small spiral of resistance wire. The coil resists the flow of electricity, and that resistance converts electrical energy into heat. The power delivered follows a straightforward relationship: power equals the voltage squared divided by the coil’s resistance. A lower-resistance coil draws more current and produces more heat, while a higher-resistance coil produces less.
That heat conducts outward from the wire’s surface into the surrounding liquid. Once the liquid reaches its effective boiling point, it transitions from liquid to aerosol: a suspension of tiny droplets carried in air. The ideal coil temperature for most e-liquids falls between roughly 200°C and 255°C (about 390°F to 490°F). Most users find temperatures above 255°C uncomfortably hot.
This is fundamentally different from smoking. A lit cigarette burns tobacco at temperatures exceeding 800°C, producing thousands of combustion byproducts including tar, carbon monoxide, and cancer-causing nitrosamines. An e-cigarette never ignites anything. It simply heats liquid until it boils.
What the Wick Does
The wick is a strip of absorbent material threaded through or wrapped around the coil. Its job is to keep a steady film of liquid on the coil’s surface so every puff produces consistent vapor. Most modern devices use specially processed organic cotton, which absorbs liquid quickly and delivers clean flavor. Some devices use ceramic or mesh wicking materials instead, each with slightly different heat tolerance and absorption speed.
When the wick can’t resupply liquid fast enough, the coil heats dry cotton instead of wet cotton. This produces the harsh, acrid taste vapers call a “dry hit.” It’s one reason manufacturers design wicks to saturate quickly and why users are told to let a new coil soak before using it.
What’s in the Liquid
E-liquid has a simple base: propylene glycol (PG) and vegetable glycerin (VG), both common food-grade compounds. Nicotine and flavoring chemicals are dissolved into this base. Commercial e-liquids typically range from a 70/30 PG-to-VG ratio all the way to pure VG with no PG at all.
PG is thinner and carries flavor well. It also produces a stronger sensation in the throat, similar to the “hit” smokers associate with cigarettes. A 70/30 PG/VG liquid rates significantly higher for throat hit than a 50/50 blend. VG is thicker and sweeter, and vapers commonly associate it with denser clouds, though controlled studies have found that users don’t consistently rate higher-VG liquids as producing more visible vapor than lower-VG ones. The perception may come more from how the thicker liquid interacts with specific devices than from VG itself.
How Nicotine Gets Into Your Body
Nicotine in e-liquid comes in two forms: freebase nicotine and nicotine salts. The difference matters because it changes how quickly nicotine enters your bloodstream and how the vapor feels in your throat.
Freebase nicotine is the older format. It’s an uncharged molecule that, in theory, crosses the membranes of the respiratory tract easily. Traditional cigarette manufacturers even added alkaline compounds like ammonia to shift nicotine toward this freebase form for faster absorption. Early e-liquids used the same approach.
Nicotine salts, popularized by JUUL’s parent company around 2015, take the opposite approach. They pair nicotine with a mild acid (like benzoic acid) to create a charged, protonated molecule. This makes the vapor smoother at high nicotine concentrations, so users can inhale more nicotine per puff without the throat burn. Clinical data from PAX Labs showed that a 2% nicotine salt solution delivered roughly three times the peak blood nicotine level of a 2% freebase solution using the same puff pattern. Multiple studies have since confirmed that nicotine salts produce higher and faster nicotine absorption than freebase nicotine at equal concentrations.
This is why most small, pod-style devices use nicotine salts at concentrations of 20 to 50 mg/mL, while larger, more powerful devices tend to use freebase nicotine at lower concentrations of 3 to 6 mg/mL.
Two Ways to Fire the Device
E-cigarettes use one of two activation methods. Button-activated devices require you to press and hold a button while inhaling. This gives you direct control over when the coil heats and for how long.
Draw-activated devices have no button. Instead, a small airflow sensor inside the device detects the pressure change when you inhale. That pressure change closes a circuit and sends power to the coil automatically. It’s simpler and more intuitive, which is why most disposable and pod-style devices use this design. The trade-off is occasional false triggering from wind or sudden pressure changes, though this is rare with modern sensors.
How Advanced Devices Manage Power
Basic e-cigarettes deliver a fixed voltage from the battery to the coil. More advanced devices, often called regulated mods, let you adjust the experience in two ways.
Variable wattage mode lets you set a specific power output. The device’s internal chip then adjusts the voltage automatically to maintain that wattage as the battery drains. Higher wattage means more heat, more vapor, and warmer inhales.
Temperature control mode works differently. You set a target temperature, and the chip continuously adjusts power to keep the coil at that temperature. This prevents the coil from ever getting hot enough to burn the wick, eliminating dry hits entirely. It also keeps each puff consistent regardless of how fast you’re inhaling or how much liquid is left on the wick.
What Happens to the Aerosol After You Exhale
The cloud you see when someone exhales isn’t smoke. It’s an aerosol made almost entirely of propylene glycol and vegetable glycerin droplets. Unlike cigarette smoke, which lingers in a 35-cubic-meter room for roughly 1.4 hours, e-cigarette aerosol dissipates in about 10 to 20 seconds. The droplets evaporate rapidly because they’re made of volatile compounds rather than the solid particulate matter found in combustion smoke.
E-cigarette aerosol does contain some harmful compounds, including formaldehyde, acetaldehyde, and trace metals, but at notably lower concentrations than conventional cigarette smoke. Cigarette smoke also generates roughly 85% of its total emissions as sidestream smoke, the wisp that curls off the lit end between puffs. E-cigarettes produce no sidestream emissions at all since the coil only heats when activated.
When Harmful Byproducts Form
The cleanliness of the aerosol depends heavily on temperature. At normal operating temperatures where the coil stays in contact with liquid, the process is relatively straightforward evaporation. But when oxygen is available and temperatures climb, the PG and VG base can break down chemically. Research has shown that both propylene glycol and glycerin begin degrading at temperatures as low as 133°C to 175°C when oxygen is present over extended heating periods, producing formaldehyde, acetaldehyde, formic acid, and acrylic acid through reactions triggered by oxygen molecules.
The more significant breakdown happens between 300°C and 400°C, which can occur during a dry hit when the coil has no liquid contact and overheats. This is another reason temperature control and proper wicking matter: keeping the coil wet and within its intended temperature range reduces the formation of these toxic byproducts substantially.