E-cigarettes are battery-powered devices that heat a liquid into an aerosol you inhale. Unlike traditional cigarettes, they don’t burn tobacco. Instead, they vaporize a solution that typically contains nicotine, flavorings, and a few base ingredients. They go by many names: vapes, vape pens, pod systems, mods, and electronic nicotine delivery systems (ENDS). Despite the variety of shapes and sizes, they all work on the same basic principle.
How an E-Cigarette Works
Every e-cigarette has three core parts: a battery, an atomizer, and a tank or cartridge that holds the liquid. The battery powers a small heating element inside the atomizer, which is typically a coil of thin wire wrapped around a wick. When you take a puff (or press a button, depending on the device), the coil heats up, the wick draws liquid toward it, and the liquid turns into an inhalable aerosol. What looks like “smoke” is actually a fine mist of tiny droplets.
The heating coils are usually made from nichrome, an alloy of chromium and nickel. Some newer devices use coils containing iron, copper, or manganese. The wick is typically silica, and the various internal joints may be brazed with brass or soldered with tin. These material details matter because, as we’ll cover below, trace metals from these components can end up in what you inhale.
What’s in the Liquid
E-liquid (also called vape juice) has four main ingredients: propylene glycol (PG), vegetable glycerin (VG), food-grade flavorings, and nicotine. PG and VG form the base of the liquid, usually in a 50:50 or 70:30 ratio. PG is thinner and carries flavor more effectively. VG is thicker and produces larger, denser clouds of vapor. Nicotine-free options exist, but most products contain nicotine.
Nicotine concentration varies widely depending on the type of device and the form of nicotine used. Open-system devices with refillable tanks typically use freebase nicotine at concentrations around 3 to 18 mg/mL. Pod-based systems use nicotine salts, a chemically modified form that delivers higher concentrations without the harsh throat hit. Pod devices commonly contain 20 to 50 mg/mL of nicotine salts. For context, a freebase concentration of 6 mg/mL produces a throat sensation similar to 20 to 25 mg/mL of nicotine salts, so the two forms aren’t directly comparable by the numbers alone.
Types of Devices
E-cigarettes have evolved through several generations, and the current market includes a wide range of form factors:
- Disposables come pre-filled and pre-charged. You use them until the liquid or battery runs out, then throw them away. They’re the simplest option and require no setup.
- Pod systems use small, snap-in cartridges (pods) that contain the liquid and atomizer. The battery is rechargeable, and you replace the pod when it’s empty. These are compact, often resembling a USB drive or a small rectangular device.
- Vape pens are cylindrical, slightly larger devices with a refillable tank and a rechargeable battery. They offer more control over liquid choice.
- Mods (short for “modified”) are the largest category. They have adjustable power settings, replaceable batteries, and large refillable tanks. These are designed for experienced users who want to customize their experience.
What’s Actually in the Aerosol
Although e-cigarette aerosol contains far fewer compounds than cigarette smoke, it is not harmless vapor. Researchers at Johns Hopkins found that a portion of tested e-cigarette samples exceeded health-based inhalation limits for nickel, chromium, lead, manganese, and arsenic. These metals leach from the heating coils and internal components into the aerosol. Pod systems and disposables had significantly higher levels of cobalt, which is toxic to lung tissue, and nickel, which is a known carcinogen.
The aerosol can also contain volatile compounds that form when the liquid is heated. The specific chemicals and their concentrations depend on factors like coil temperature, how often you puff, and the composition of the liquid itself.
How Vaping Compares to Smoking
Because e-cigarettes don’t burn anything, they eliminate the combustion process that generates most of the cancer-causing chemicals in cigarette smoke. A large meta-analysis published in Frontiers in Pharmacology found that people who completely switched from cigarettes to e-cigarettes had significantly lower levels of eight different carcinogen biomarkers in their bodies. The reductions ranged from roughly 54% to as much as 97% depending on the specific compound measured.
This does not mean vaping is safe in absolute terms. It means the exposure profile is substantially different from, and lower than, smoking combustible cigarettes. For someone who has never smoked, picking up an e-cigarette still introduces nicotine dependence and chemical exposures that wouldn’t otherwise exist.
Lung Injury Risk: EVALI
In 2019, a wave of severe lung injuries linked to vaping products drew national attention. The CDC designated the condition EVALI (e-cigarette, or vaping, product use-associated lung injury). Among diagnosed patients, 95% experienced respiratory symptoms like coughing, chest pain, and shortness of breath. About 77% also had gastrointestinal symptoms, including nausea, vomiting, and diarrhea. In some cases, the stomach symptoms appeared before the breathing problems. Fever, chills, and weight loss accompanied these symptoms in 85% of patients.
EVALI was primarily associated with vaping products containing vitamin E acetate, an additive used as a thickener in black-market THC cartridges. Cases dropped sharply after public health warnings, but the outbreak highlighted the risks of using unregulated or counterfeit vaping products.
Battery Safety
E-cigarette batteries, like other lithium-ion batteries, can overheat and in rare cases catch fire or explode. The FDA notes that while these incidents appear uncommon, they can cause serious injury to the user and bystanders. The exact causes aren’t fully understood, but battery-related issues, such as using damaged batteries, improper charging, or carrying loose batteries near metal objects like coins or keys, are suspected contributors.
Regulation in the United States
The FDA regulates e-cigarettes as tobacco products. Manufacturers must submit a premarket tobacco product application (PMTA) to legally sell their devices in the U.S. As of the latest data, only 41 e-cigarette products have received FDA marketing authorization. These are the only ones that may be lawfully sold in the country. In practice, thousands of unauthorized products, particularly disposables imported from overseas, remain widely available despite enforcement efforts.