The chemical composition of the electronic cigarette aerosol varies across and within manufacturers. Limited data exists regarding their chemistry. However, researchers at Johns Hopkins University analyzed the vape clouds of popular brands such as Juul and Vuse, and found "nearly 2,000 chemicals, the vast majority of which are unidentified."

An electronic cigarette (e-cigarette) or vape is a device that simulates tobacco smoking. It consists of an atomizer, a power source such as a battery, and a container such as a cartridge or tank. Instead of smoke, the user inhales vapor. As such, using an e-cigarette is often called "vaping". The atomizer is a heating element that vaporizes a liquid solution called e-liquid, which quickly cools into an aerosol of tiny droplets, vapor and air. The vapor mainly comprises propylene glycol and/or glycerin, usually with nicotine and flavoring. Its exact composition varies, and depends on several things including user behavior.