The government’s top doctor has urged parents and government officials to take immediate action to stop millions of teens from becoming addicted to vaping after figures showed high-school students are taking up the habit in record numbers. In a rare public warning, Surgeon General Jerome Adams said Tuesday that parents, teachers, health professionals, and government officials must take “aggressive steps” to keep teenagers from using e-cigarettes. He said that, among teens, “nicotine is dangerous and it can have negative health effects... It can impact learning, attention and memory, and it can prime the youth brain for addiction.” There has been an explosion in teen vaping over the past year and officials fear its rise in popularity could undermine decades of declines in tobacco use. An estimated 3.6 million U.S. teens are now using e-cigarettes, according to the latest federal figures. Survey results released Monday showed twice as many high-school students used e-cigarettes this year compared to last year.