Scientists have cautioned about the dangers of e-cigarettes. Now they are concerned the products contain cancer-causing chemicals, according to a new report.

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Researchers from the University of California at San Francisco recently conducted a study, published in Pediatrics, to determine the toxins associated with e-cigarette use particular among teens.

To do so, they examined the urine from about 100 adolescents with an average age of 16.4. Sixty-seven of them only used e-cigarettes, 17 used e-cigarettes and traditional tobacco and 20 were nonsmokers.

After analyzing the results, they found toxic compounds were three times higher for those who smoked e-cigarettes, compared to the nonsmokers. The toxic compounds were three times higher for e-cigarette and cigarette users, compared to e-cigarette smokers only.

The list of compounds include acrylonitrile, acrolein, propylene oxide, acrylamide and crotonaldehyde, which have all been linked to cancer.

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"Teenagers need to be warned that the vapor produced by e-cigarettes is not harmless water vapor, but actually contains some of the same toxic chemicals found in smoke from traditional cigarettes," lead author Mark Rubinstein said in a statement. "Teenagers should be inhaling air, not products with toxins in them."

The researchers also pointed out that toxic chemicals, particularly propylene glycol and glycerin, were found in the bodies of those who used flavored e-cigarettes without nicotine.

Although propylene glycol and glycerin, which liquefies the e-cigarette products, have been approved by the Food and Drug Administration, they produce potentially harmful substances when heated for vaporization.

Scientists now plan to continue their investigations to further understand the damaging effects e-cigarettes may have on youth and adults. They hope their findings will warn teens of the risks as well.

“E-cigarettes are marketed to adults who are trying to reduce or quit smoking as a safer alternative to cigarettes,” said Rubinstein. “While they may be beneficial to adults as a form of harm reduction, kids should not be using them at all.”

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