E-cigs(pen style) are pre loaded cartridges filled with liquid which BTW are produced by Big Tobacco companies
Studies done have shown those aren't necessarily the safest do to what is in the pre filled cartridges
http://www.m.webmd.com/a-to-z-guides/features/electronic-cigarettes
Vaping is totally different as you have a tank / RDA (rebuildable dripping atomizer) which you add your own liquid(juice) which produce much more vapor(faster nicotine absorption)
Ingredients in e-liquid are propylene glycol, vegetable glycerin(which is in most processed food products), may contain nicotine, and natural and /or artificial food flavoring
As with anything we do in life all have their inherent risks involved
Many studies have been done by Big Tobacco, New EnglandJournal of Medicine, American Lung Association and many others
I'm not going to deny the fact that it is completely safe but there are way less chemicals in the "juice" as opposed to the 1000's in a cigarette
Diacytel and other harmful ingredients have been found in those pre filled cartidges which seems to be the main debate over safety
https://en.m.wikipedia.org/wiki/Safety_of_electronic_cigarettes
I have been vaping for several years and was a pack a day smoker for 15plus years
My breathing had greatly improved -no more hacking up my lungs every morning plus it is much more cost effective -$30 every few months vs $30 a week
Out of all the wonderful ladies I have met only 1 objected to my vaping
Many are very inquisitive and a few have actually tried it
All have complemented the pleasant smell over funky stinky cigarette