How do they work?

Electronic cigarettes are battery-operated devices that heat a liquid solution (usually but not always containing nicotine), turning it into a vapor that can be inhaled. They are often called e-cigarettes, e-vaporizers or electronic nicotine delivery systems. Using e-cigarettes is often referred to as vaping.

Some e-cigarettes resemble traditional cigarettes, cigars or pipes. Others look like pens or flash drives or have completely different designs. E-cigarettes can be disposable or refillable. Most use a cartridge — disposable cartridges are sometimes called pods — or have a refillable reservoir or "tank" to hold the liquid, also called e-liquid or e-juice. The liquid typically contains nicotine, flavorings, propylene glycol and vegetable glycerin.

The strength of an e-cigarette is determined by the amount of nicotine in the e-liquid and is expressed in milligrams per milliliter or as a percentage. However, studies have raised concerns that product labels don't always provide accurate information about nicotine content. Some pods contain a concentrated form of nicotine called nicotine salt. A pod containing 5% nicotine salt may have as much as 30 to 50 milligrams of nicotine, the equivalent amount of nicotine delivered in one to three packs of cigarettes.