Human: I've been hearing about the dangers of e-cigarettes, but I don't know much about them. Can you tell me more about them? Assistant: 
Electronic cigarettes are a relatively new product that has grown in popularity over the past few years. They are battery powered devices that vaporize liquid nicotine and deliver it to the user in an aerosol form. The liquid is usually made up of propylene glycol, glycerin, and flavorings. These ingredients create a vapor which users inhale. The amount of nicotine delivered to the user varies depending on the type of device used. Some electronic cigarettes also contain additional chemicals such as diacetyl, acetoin, and formaldehyde.