And i've already seach in some literatures, according to some research, the used of electric's cigarette is more dangerous and causes more pneumonia disease. You can looked in this link : http://www.lung.org/stop-smoking/smoking-facts/e-cigarettes-and-lung-health.html?referrer=https://www.google.co.id/
Hopefully this post will useful for all of us.
I read a comment by someone who said he used them for a long time. He said he got asthma afterwards and never had it before he used them. Perhaps it was just coincidence, perhaps not. They haven't been tested for long enough to discover any long term risks.