Despite being on the market for several years, many regulatory agencies and health experts aren't sure just how safe e-cigarettes actually are. Among their concerns is the lack of disclosure of all the ingredients used as well as the lack of (or validity of) health and safety claims by manufacturers about their products. In 2009, for example, the Food and Drug Administration (FDA) found some cartridges of liquid nicotine contained about 1 percent diethylene glycol (DEG), a toxic chemical ingredient also found in antifreeze [source: FDA].
To make matters worse, the amount of nicotine listed on a cartridge label may not match the actual amount in the cartridge. FDA testing has found cartridges under the same manufacturing label may release significantly different levels of nicotine, ranging from 26.8 to 43.2 micrograms nicotine per 100 milliliter puff. And those nicotine-free cartridges? Lab tests indicate you're still getting a low dose, despite the claims [source: FDA].