U.S. health officials said Wednesday they have found cancer-causing ingredients in electronic cigarettes, despite manufacturers' claims the products are safer than tobacco cigarettes.

The Food and Drug Administration said testing of products from two leading electronic cigarette makers turned up several toxic chemicals, including a key ingredient in antifreeze.

Fe Miao Nan, executive director of Ruyan Group Ltd. smokes an electronic cigarette during an interview at his office in Beijing, China, Tuesday, Feb. 17, 2009. Ruyan Group Ltd, Beijing-based company was the first to develop electronic cigarettes and says its patented atomizer technology allows users to get an immediate nicotine fix without being harmed by the hazardous chemicals produced when tobacco is burned. (Andy Wong/Associated Press)

"Little is known about these products, including how much nicotine is there and what other chemicals may be there," FDA deputy commissioner Dr. Joshua Sharfstein said.

Electronic cigarettes produce a nicotine mist absorbed directly into the lungs. Most can easily pass as a tobacco cigarette with slim white bodies and glowing amber tips. They even emit what look like puffs of white smoke.

Manufacturers have touted the products as a healthier alternative to smoking because there is no burning involved, and they don't contain the same hazardous cocktail of cancer-causing chemicals.

But FDA scientists said that when they tested 19 varieties of cigarettes, half of them contained forms of nitrosamine, a carcinogen known to cause cancer in humans. Many products that claimed to contain no nicotine actually had low levels of the stimulant. The products are made primarily in China.

Agency officials said the "quality control processes used to manufacture these products are inconsistent or nonexistent."

Brands tested by the agency included Smoking Everywhere, marketed by a Florida-based company, and NJoy Cigarettes, based in Scottsdale, Ariz.

The Electronic Cigarette Association said the FDA's testing was too narrow to reach "any valid and reliable conclusions."

NJoy, meanwhile, said it was confident its products were "appropriate alternatives" for smokers.

"NJoy's products have been on the market since at least April 2007 with no reports of adverse health consequences," it said.

'Gateway' product

Public health advocates have complained the products are aimed at young people and can serve as a "gateway" to tobacco smoking. Many come in flavours, including chocolate, bubblegum and mint.

"Tobacco industry research has demonstrated that fruit and candy flavours increase the social acceptance of cigarettes and curiosity to try the product," said Dr. Jonathan Winickoff, chair of the American Academy of Pediatrics' Tobacco Consortium.

Electronic cigarettes include a light that glows as the user sucks on it, and a nicotine vapour that looks like smoke.

Because electronic cigarettes are not covered by federal tobacco laws, they are also often easier for young people to buy. The Electronic Cigarette Association, however, said its members were only marketing their products to long-time, adult smokers.

Regulators said they have halted 50 shipments of electronic cigarettes at ports and borders since last summer. The FDA said it is authorized to seize the products because — for legal purposes — they are a medical device used to deliver nicotine.

However, the FDA's enforcement attempts have been challenged in federal court by manufacturers.

FDA officials declined to comment on whether they would take action against the two manufacturers whose products were tested.

The agency did say it's "planning additional activities" to address safety issues with the products, which may include recalls or criminal sanctions.

In an effort to move beyond cigarettes, tobacco companies have introduced a number of smokeless products to keep smokers as buyers of other items. They are trying to convert smokers to products such as moist snuff, chewing tobacco and snus — teabag-like pouches that users stick between their cheek and gum.