I would suggest you read this thread on WebMD on the topic:
http://forums.webmd.com/3/smoking-cessation-exchange/forum/342?@530.BYzcag5IdK8 @
But to answer your question, the 4 main ingredients in the eliquid are: water, food grade flavorings, propylene glycol and nicotine (optional). All are generally safe for human consumption. Remember, nicotine is not a carcenagentic substance. It's the other things in cigarette smoke that causes diease which personal vaporizers do not have.
If you are struggling to quit, then you ought to look into vaping. Just make sure you get a good one and not one of the over priced ones like from the mall or the ones that are highly marketed, like Blu or SafeCig - they are "crap". Here is what I replied to someone in the other thread that may be helpful:
The mall PV's (personal vaporizers) are basically "crap". Here are 2 very good "beginner" PV's and one that is a little more advanced:
E-Power:
http://www.madvapes.com/e-Power_c_231.html RIVA 510 or 901:
http://www.liberty-flights.com/product.asp?id=55 5 volt GLV2:
http://greatlakesvapor.com/ You always want to get manual batteries and one with a little larger battery. I would suggest starting with 24mg nicotine strength and adjusting up or down to suit your need to make the transition. Remember:
Rule of Thumb: the more it looks like the real thing, the worse the performance. I would also suggest you check out the largest site for information on vaping:
http://www.e-cigarette-forum.com/forum/ Also check out this site for good safety information on vaping:
http://casaa.org/member.asp