What are electronic cigarettes?
From Safer nicotine wiki
E-cigarettes are battery powered devices that work by vaporizing a solution of propylene glycol and/or vegetable glycerin, and flavoring. The solution is often referred to as “e-liquid” and usually includes nicotine, but that is optional. The result is something that feels somewhat like smoke in the mouth and lungs, but without involving any real smoke or combustion. Read more here.