The debate over electronic cigarettes is heating up as more and more people are using to help them quit tobacco, even though the devices are not approved for smoking cessation by the Food and Drug Administration (FDA).

One side in the debate argues that e-cigarettes could be the beginning of the end of smoking in America, a disruptive innovation that could make cigarettes obsolete. The other side is convinced that e-cigarettes may erase the hard-won progress achieved over the last half-century in reducing smoking, and predict that the modern gadgetry will be a glittering gateway to the deadly, old-fashioned habit for children, and that adult smokers will stay hooked longer now that they can get a nicotine fix at their desks.

The devices, intended to feed nicotine addiction without the toxic tar of conventional cigarettes, have divided a normally sedate public health community that had long been united in the fight against smoking and Big Tobacco.

The essence of the disagreement comes down to a simple question: Will e-cigarettes cause more or fewer people to smoke?

Science that might resolve questions about e-cigarettes is still developing, and many experts agree that the evidence so far is too skimpy to draw definitive conclusions about the long-term effects of the devices on the broader population.

Soon, the Food and Drug Administration is expected to issue regulations that would give the agency control over the devices, which have had explosive growth virtually free of any federal oversight.

Pessimists say that while e-cigarettes might be good in theory, they are bad in practice. The vast majority of people who smoke them now also smoke conventional cigarettes. E-cigarettes may even prolong the habit, by offering a dose of nicotine at times when getting one from a traditional cigarette is inconvenient or illegal.

Nicotine, the powerful stimulant that makes traditional cigarettes addictive, is the crucial ingredient in e-cigarettes.  It is inhaled through a liquid that is heated into vapor.  The liquids come in favors like mango and watermelon.  There is concern that the vapor is a lung irritant, and the effects of inhaling it over time are unknown.