The CDC found e-cig usage jumped from around 10 percent in 2010 to more than 21 percent in 2011 among adults who already smoked conventional cigarettes. E-cigarettes deliver a fraction of the nicotine that cigarettes doroughly 20 percent (between 0 and 35 mg of nicotine per puff) of what a regular cigarette delivers. A recent study found that the vapors can damage the developing lungs of America’s youth: The vapors are probably not the most sensitive to the effects of exposure to second-hand aerosol.”]
Source: https://gizmodo.com/why-e-cigarettes-might-not-be-as-safe-as-you-think-1589485508