Researchers have warned of the health risks of electronic cigarettes, increasingly popular among smokers who want to quit the habit or at least smoke less.

E-cigarettes look like the real thing but consist of a rechargeable battery, a cartridge and a mouthpiece. The e-cigarettes are said to have no tobacco, offering an alternative to the nicotine patch or gum.

With the U.S Food and Drug Administration deciding that e-cigarettes will be labeled as tobacco products and not as drug-delivery devices, manufacturers will be able to sell the products straight to consumers, according to a report published in the latest issue of the New England Journal of Medicine.

It was written by Nathan K. Cobb, a pulmonologist and assistant professor at Georgetown University Medical Center and David B. Abrams, an executive director of the Schroeder Institute.

They also said that prominent cigarette manufactures such as Philip Morris International and British American Tobacco are likely to come out with even more sophisticated nicotine inhalers in the future.

They also noted that the cartridge can be replaced by the user giving he or she control over the amount of nicotine put in.

Supporters of the e-cigarette argue that the products help people avoid smoking regular cigarettes.

But scientists and consumer groups have raised concerns about their potential harm to health. The electronic butts produce a propylene glycol mist and include other chemicals which have not been tested properly.

The two authors said there are other substitutes such as nicotine patches and gum, approved by the FDA.

They added that smokers who want to quit can avail of other services such as telephone quit lines, although not starting smoking in the first place is best.