This question is very easy to answer in some ways and difficult in others. The problem with the question is it contains an absolute. The absolute being "harmless" as opposed to "less harmful" or "relatively harmless" both of which I would feel more comfortable with supporting. The problem with absolutes is that almost nothing can truly live up to them. I would not like to say that the air we breathe, or the water we drink is "harmless".
The air we breathe in the UK is probably less harmful (Depending on exactly where in the UK) than it is in a major industrial areas in southern China. The water we drink is certainly less harmful than stagnant pond water. I would not however want to nominate either as "harmless" in absolute terms.
It is also a little difficult to talk about whether the nicotine in a traditional cigarette is in itself any more harmful than the Nicotine in an Electronic cigarette. In truth it is the same. It has never been suggested that the harm caused by traditional cigarettes is in any way connected with the nicotine. Yet the nicotine is the addiction and the reason people continue to smoke, or vape.
Nicotine in itself, so long as it is not ingested through the digestive system or absorbed through the skin, is generally believed to be no more, or less harmful than caffeine.
Therefore there is no difference in the actual nicotine derived harm in an ecig or a traditional cigarette. Truthfully it doesn't matter. It doesn't matter because although nicotine has always been the reason people smoke, it has never been suggested that it causes any significant harm to the smoker. The harm from smoking a traditional cigarette has always been directly as a result of the burning process.
In an electronic cigarette, there is no burning process, so there is none of the harm derived from such a process. Find out what is an electronic cigarette in our history page.
Nicotine itself is probably not the drug equivalent of Mother Theresa, I am sure however that without even trying I could list twenty other drugs and substances we consume on a daily basis, without giving any thought, which are significantly more harmful than Nicotine.
If the reason for the question, which is at the top of this article, is to work out if Electronic Cigarettes are less harmful than traditional cigarettes, then the answer is simple, a no brainer. No burning, no carbon Monoxide, no tar and no noxious chemical to assist the burning process and speed, therefore much less harm. Massively less harm, not even on the same harm planet.
If however we are comparing the nicotine itself. Inhaled nicotine is generally considered about as harmful as a cup of coffee. It makes no difference how you inhale it, give that the quantities are the same.
However add the burning process and inhale the smoke and suddenly you have a life threatening situation.
So forget Nicotine, it is a red herring. Don't smoke, Vape. You know it makes sense!