SACRAMENTO, Calif. — California's top health official Ron Chapman on Wednesday slammed electronic cigarettes as a growing health threat and announced plans for a public awareness campaign.

Some things to know about the concerns of e-cigarettes raised by health advocates:

WHAT ARE E-CIGARETTES?

They are electronic devices that heat liquid nicotine derived from tobacco into an inhalable vapor available in fruity and sweet flavors. Traditional cigarettes burn tobacco leaves, which also releases tar and carcinogenic chemicals. Paper cigarettes are single use and burn within minutes, but e-cigarette cartridges contain different levels of nicotine and can last for days depending on how often users puff. Using e-cigarettes is known as vaping.

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WHAT ARE THE HEALTH RISKS?

Many of the long-term effects of e-cigarettes are not known because the technology is recent and research is ongoing. But Chapman says enough studies suggest the products are harmful to curtail their use. E-cigarettes emit at least 10 chemicals known to cause cancer or birth defects, according to a California health department report released Wednesday. The report does not say if these are released at levels that threaten health, but Chapman says some chemicals such as formaldehyde are never safe. Nicotine is also harmful to youth brain development. While e-cigarette makers tout the product as safer than combustible cigarettes, the California report says there is no evidence the device helps people quit smoking.

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HOW POPULAR ARE E-CIGARETTES?

Surveys of students show teenagers already are choosing vaping over smoking. Last year, 17 percent of high school seniors reported using e-cigarettes compared with 14 percent using cigarettes. Use is also rising among adults. In 2013, 3.5 percent of adults and 7.6 percent of young adults reported using e-cigarettes.