Harvey B. Simon, M.D.  Electronic cigarettes: Help or hazard?
There are three reasons to worry about electronic cigarettes.
First, the dose of nicotine delivered with each puff may vary
substantially. An FDA analysis recorded nicotine doses between
26.8 and 43.2 micrograms per puff. It also detected nicotine in
products labeled as nicotine free.  Second, electronic
cigarettes deliver an array of other chemicals, including
diethylene glycol (a highly toxic substance), various
nitrosamines (powerful carcinogens found in tobacco), and at
least four other chemicals suspected of being harmful to humans.
To be sure, the dose of these compounds is generally smaller
than found in “real” cigarette smoke. But it isn’t zero.  Third,
by simulating the cigarette experience, electronic cigarettes
might reactivate the habit in ex-smokers. They could also be a
gateway into tobacco abuse for young people who are not yet
hooked.  We need scientific studies of e-cigarettes. Until then,
it’s caveat emptor, buyer beware. And