E-cigarettes are nicotine delivery devices and nicotine promotes cancer growth. And yes there is secondary inhalation with e-cigarettes. You probably would not call it secondary smoke, but whatever is being vaporized by the e-cigarette gets exhaled by the user and then inhaled by other non-users in the area. I worked closely with an e-cigarette smoker once and I could definitely feel it.
E-cigarette proponents say that because e-cigarettes do not burn anything, they are safer than cigarettes. That is probably true, but safer does not mean safe. They are definitely not safe as the main substance they are intended to deliver -- nicotine -- is itself unsafe.
So until there are studies that show that there is no danger to others in the environment all smoking bans should apply to e-cigarettes.
Nicotine is, itself, pretty damned safe. There is currently no epidemiological evidence to support a direct link between nicotine and cancer. There are reasons to believe it can plausibly cause cancer from animal models, but there's no good reason to think that it is more carcinogenic than a boatload of other things.
The main reason that nicotine "feels" significantly likely to cause cancer is its association with tobacco. But there's already a perfectly adequate explanation for the carcinogenicity of tobacco. So it's important to resist the affect heuristic[0] which makes us tend to find all things associated with tobacco "cancery".
In addition, it's extremely doubtful that you'd get any nicotine second-hand from someone using an e-cigarette.
Nicotine is not a carcinogen, i.e. nicotine does not promote cancer growth. The carcinogen in cigarettes is the "tar", which is absent from E-cigarettes.
Indirectly, nicotine increases cholinergic signalling (and adrenergic signalling in the case of colon cancer[77]), thereby impeding apoptosis (programmed cell death), promoting tumor growth, and activating growth factors and cellular mitogenic factors such as 5-LOX, and EGF. Nicotine also promotes cancer growth by stimulating angiogenesis and neovascularization.[78][79] In one study, nicotine administered to mice with tumors caused increases in tumor size (twofold increase), metastasis (nine-fold increase), and tumor recurrence (threefold increase).[80]
It may not cause cancer directly, but it does sound pretty toxic and does help cancer growth. There might be a "safe" upper limit at which inhaling secondary smoke from e-cigarettes would have an insignificant impact, but we need more studios.
You would probably take in more nicotine from eating a meal of eggplant than you would get from secondhand vapor. You wouldn't get enough from secondhand vapor to have psychoactive effects, let alone come anywhere near toxicity. Here is some reference to an indoor air quality showing vaping to not harm other people: www.ivaqs.com
All sorts of things we take in can "promote cancer growth". Nicotine by itself is so far from a carcinogen that IARC doesn't even investigate it as one. There are roughly 50 components of tobacco and tobacco smoke called the "Hoffman analytes" which are the carcinogens. There are studies showing the relative cardiovascular and cancer risk, and the worst carcinogens are produced by burning plant material. These are not present in ecigs.
Some studies which are dubious because of the choice of equipment and researchers not simulating the way ecigs are actually used have shown a handful of components way down the list of dangerous ingredients. Other studies have been done where these didn't even show up, but we are talking about things like formaldehyde and acetaldehyde near the level put out by smoking. If you compare the cancer risk of these to smoking, you are still looking at less than 5% of the cancer risk of smoking (probably under 1% really).
You'll be hard pressed to find anything stimulatory/anabolic that does not stimulate already existing cancers. The simplest example, protein consumption can also promote cancer growth (I can find a ref if pressed, I'm just lazy right now).
On the other hand, this study found that a high protein, low carb diet can reduce cancer growth in mice[1]. This is not to say that what you said is inaccurate. I just see your comment and the first thing I think is "uh oh, can I still eat paleo?"
Given that anabolism can promote tumor growth, do weightlifters tend to have more intense bouts of cancer?
Remember that a high protein low carb diet is significantly different from a normal high carb high protein diet.
As to the second point the best answer I can give you is maybe. Unfortunately different cancers have completely different mechanisms, while high protein may be bad for mammary cancers it might be good for bone cancers. So it's really situational.
So what you're telling me is I can't have complete knowledge or control over my life? How am I going to live forever, then??
Edit: but seriously, thanks for the response. I think a lot of people are torn by trying to make basic decisions like this, and making sense of conflicting findings is pretty frustrating. Seems like a lot of carbs is bad, though, so I'm going to go with that.
If you consider e-cigs a harm reduction device, the carcinogenic potential of standalone nicotine dwarves that of traditional cigarettes.
More research is needed but all the evidence so far points to e-cigs being safer than cigarettes for those who can not kick the habit. But the passive smoking impact is a very valid point and needs to be studied.
It shows that the amount of passive vapor is extremely low. Though it should be mentioned that it was commissioned by flavourart, a major eliquid producer.
E-cigarette proponents say that because e-cigarettes do not burn anything, they are safer than cigarettes. That is probably true, but safer does not mean safe. They are definitely not safe as the main substance they are intended to deliver -- nicotine -- is itself unsafe.
So until there are studies that show that there is no danger to others in the environment all smoking bans should apply to e-cigarettes.