Human: I've been hearing a lot about e-cigarettes. What are they and are they safe? Assistant: 
E-cigarettes are devices that use an electric current to vaporize a solution containing nicotine, propylene glycol, and/or vegetable glycerin. They are designed to simulate the act of smoking without the smoke or ash. The solutions used in e-cigarettes typically contain fewer harmful chemicals than traditional cigarettes, making them potentially less harmful than regular cigarettes. However, there is still limited research on the long-term health effects of using e-cigarettes.