The shares of U.S. adults who perceive e-cigarettes to be as harmful as or more harmful than traditional cigarettes have notably increased in recent years, a new study finds, raising concern some smokers may be deterred from switching to electronic devices that in the short term appear to be a healthier option.

"Our findings underscore the urgency to convey accurate risk information about e-cigarettes to the public, especially to adult smokers who are unable or unwilling to quit smoking, and therefore could benefit most by switching from cigarettes to e-cigarettes," the study authors say.

For the study, researchers affiliated with Georgia State University and the University of Oregon analyzed data from two large, nationally representative surveys that dealt with attitudes and perceptions surrounding e-cigarette products. From both data sets, they found that the proportion of adults in the U.S. who perceived e-cigarettes as less harmful than cigarettes declined – from 39.4 percent in 2012 to 33.9 percent in 2017 in one, and from 50.7 percent in 2012 to 34.5 percent in 2017 in the other.

Meanwhile, the share of adults who perceived e-cigarettes to be as harmful as cigarettes increased between the same two years, from 11.5 percent to 36.4 percent and from 46.4 percent to 55.6 percent, respectively. In addition, increases were seen in the share of those who viewed e-cigarettes as more harmful than traditional tobacco cigarettes, from 1.3 percent to 4.3 percent and from 2.8 percent to 9.9 percent.

The shift in public perception to a more negative outlook on the health risks of using e-cigarettes may "reflect consumers’ concerns about the risk of addiction and/or the uncertainty about e-cigarette’s long-term health effects," the study says, noting "the emergence of new evidence of substantial risk of heart and lung diseases associated with e-cigarette use, as well as high levels of pulmonary toxic effects in e-cigarettes."

Yet "this perception may also deter a complete switch from cigarettes to e-cigarettes among smokers," the study says. "In light of this possibility, the observed upward trend of perceiving e-cigarettes to be as harmful as or more harmful than cigarettes among U.S. adults warrants heightened attention."

"Although the long-term health effects of e-cigarettes are still unknown, growing evidence and consensus among scientists and researchers suggest that the short-term health risks of completely switching to e-cigarettes are substantially less than those of continued smoking for adults who are unable or unwilling to quit cigarette smoking," the study says.

In an editorial accompanying the study, Stanton Glantz, the Truth Initiative distinguished professor of tobacco control at the University of California–San Francisco, also notes emerging evidence of multiple risks tied to e-cigarettes, and says an increase in the perceived risks of e-cigarettes is "an important element for curbing their use by youth."

"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," he writes. "From this perspective, the declining public perception that e-cigarettes are less harmful than cigarettes is a good thing that may turn out to be where the scientific consensus lands as the new evidence on the harms of e-cigarettes continues to accumulate."