An e-cigarette works by vaporizing a liquid that's based on nicotine salts and natural flavourings. When you smoke your device, you inhale the vapour, not the product of burning. And it is for the smouldering tobacco that conventional cigarettes are so condemned.
Only the nicotine contained in the devices can cause harm, as it is also addictive and excites the nervous system and increases blood pressure. If you have a medical contraindication to such exciters, natural oils or salt nicotine, it is best to avoid using vapes.