The researchers examined data from the Tobacco Products and Risk Perceptions Survey, administered by the Georgia State University Tobacco Center of Regulatory Science, and the Health Information National Trends Survey, administered by the National Cancer Institute; both are nationally representative surveys administered to US adults every year when the results of both surveys were combined, the percentage of people who believed that e-cigarettes were less harmful than regular cigarettes decreased from 45% in 2012 to 35% in 2017. The number of people who thought e-cigarettes were as harmful as cigarettes increased to 45% in that time, and the percentage who believed that e-cigarettes were more harmful remained low, at less than 10%, according to the results, published Friday in JAMA. 

The findings "underscore the urgent need to accurately communicate the risks of e-cigarettes to the public," the authors note, expressing concern that as greater numbers of people view e-cigarettes as more harmful than cigarettes, they will be less willing to make the transition from one to the other. Electronic cigarettes work by heating a pure liquid called e-juice -- composed of flavorings, propylene glycol, glycerin and often nicotine -- until it vaporizes. The resulting vapor is much less offensive to both smokers and non-smokers. In 2017, the National Academy of Science, Engineering, and Medicine concluded that "e-cigarettes pose less risk to an individual than combustible tobacco products." 

Since then, however, studies have linked the use of e-cigarettes with an increased risk of heart attack, stroke, chronic obstructive pulmonary disease and other respiratory diseases at rates similar to those of traditional cigarettes in some cases, explained Stanton A. Glantz, a professor at the University of California, San Francisco Center for Tobacco Control Research and Education, in an editorial published alongside the study in JAMA. The vision of those whom Glantz describes as "e-cigarette optimists" is for smokers to switch completely from cigarettes to e-cigarettes, he said. But contrary to their hopes, about two-thirds of adult e-cigarette users continue to use both."The risks of e-cigarette use are in addition to any risks from combustible cigarettes," he added, meaning that people who use both have higher risks of heart disease and lung disease than those who smoke only regular cigarettes. 

As the long-term effects of e-cigarette use continue to be understood, the changing public perception of risk may benefit one group of people the most: teens and young adults.

Youth who have negative views of e-cigarettes are less likely to use them, which is important for curbing use in this group, Glantz said."In terms of overall public health effects, this explosion of youth use swamps any potential harm reduction that may accompany adults switching from cigarettes to e-cigarettes."