The increasing popularity of e-cigarettes — known in academic parlance as ENDS, for electronic nicotine delivery systems — has policymakers in something of a quandary, as they struggle to understand the products' pros and cons. That debate, as the World Health Organization noted in a report to an international tobacco control convention in September 2014, has become increasingly divisive. One underlying challenge is that, with e-cigarettes invented only about a decade ago, their long-term health implications remain unclear — compared with vast amounts of research on the dangers of conventional smoking. For example, while some studies have found that the devices deliver just a tenth of the carcinogenic compounds of regular cigarettes, others have found them to contain higher levels of potentially harmful metals such as nickel and chromium. "Whereas some experts welcome ENDS as a pathway to the reduction of tobacco smoking, others characterize them as products that could undermine efforts to denormalize tobacco use," the WHO stated, adding that e-cigarettes "represent an evolving frontier, filled with promise and threat for tobacco control."In mid-April, the Centers for Disease Control and Prevention reported a startling statistic: in just a single year, the use of electronic cigarettes among middle and high school students more than tripled. The numbers, from the 2014 National Youth Tobacco Survey, mean that some 2.5 million teens nationwide are using the devices, which turn liquid nicotine into an aerosol that's inhaled — a process commonly known as "vaping." "This is the first time since the survey started collecting data on e-cigarettes in 2011 that current e-cigarette use has surpassed current use of every other tobacco product overall," the agency noted in its Morbidity and Mortality Weekly Report, "including conventional cigarettes." Among high schoolers, the vaping rate was 13.4 percent; by contrast, 9.2 percent reported smoking cigarettes and 5.5 percent used smokeless tobacco.