The perception that e-cigarettes are less harmful than regular cigarettes fell between 2012 and 2014, a sign that fewer people see them as a safe alternative to smoking tobacco, a new study led by researchers at the Johns Hopkins Bloomberg School of Public Health suggests.

In 2012, the study found, half of those surveyed thought e-cigarettes were less harmful than cigarettes. By 2014, the number had dropped to 43 percent. During this period, advertisers often represented e-cigarettes as a safer alternative to traditional cigarettes, the researchers note. E-cigarettes are battery-operated devices that convert liquid containing nicotine into vapor that consumers inhale.

The study was based on the Health Information National Trends Surveys conducted by the National Cancer Institute. The nationally representative sample included smokers, former smokers and non-smokers. The study appears online in the American Journal of Preventive Medicine.

The researchers were surprised by the findings, given the mixed assessments of e-cigarettes' risk compared to traditional tobacco products. Since they were introduced to the U.S. market in 2007, the devices have been pitched to consumers as potentially safer alternatives to cigarettes, or even a harmless way to stop smoking, given that e-cigarettes contain no tobacco, a known carcinogen that also causes pulmonary and heart disease.

On the other hand, some in public health fear that e-cigarettes could become a gateway to smoking tobacco for young people. Smoking remains the leading cause of preventable death in the world.

"It's a good thing that information about e-cigarettes' possible adverse health effects has gotten out there, especially considering there wasn't a government or public health push during the study years," says study leader Eric W. Ford, PhD, MPH, a professor in the Bloomberg School's Department of Health Policy and Management. "When misinformation about health effects about any substances becomes widespread, it is usually very hard to reverse the trend. That somehow happened here."

According to the Centers for Disease Control and Prevention, 3.7 percent of U.S. adults were using e-cigarettes in 2014. E-cigarettes were more likely to be used by current cigarette smokers and former smokers who quit smoking within the past year than former smokers who quit smoking more than 1 year ago and those who had never smoked.

There is no overriding consensus among researchers about whether e-cigarettes are indeed harmful to human health. There are, Ford explains, two research knowns. On the one hand, e-cigarettes eliminate many of the carcinogenic elements associated with smoking tobacco. On the other hand, e-cigarettes may include flavorings and other ingredients containing the chemical diacetyl, which can cause bronchiolitis obliterans, or "popcorn lung," the thickening and narrowing of the airways due to scarring of the lung's air sacs. (The condition was so named because diacetyl was once used as a butter flavoring for microwavable popcorn.)

Earlier this year, in a much-anticipated move, the Food and Drug Administration announced that it would start regulating e-cigarettes the same way it regulates cigarettes - including banning their sale to anyone under age 18. The FDA has not yet proposed additional regulations around e-cigarettes. Earlier this month, in the government's strongest warning to date, the U.S. Surgeon General urged young people to avoid e-cigarettes altogether, calling them "unsafe." Among children, teens and young adults, e-cigarettes are the most commonly used nicotine product.

For the study, the researchers combined three "cycles" of data from the 2012, 2013 and 2014 Health Information National Trends Survey, an annual survey of U.S. households sponsored by the National Cancer Institute. The surveys, which included 3,630 respondents in 2012, 3,185 in 2013 and 3,677 in 2014, were made up of about 60 percent non-smokers, 20 percent former smokers and 20 percent current smokers. The study also found that awareness of e-cigarettes jumped from 77.1 percent in 2012 to 94.3 percent in 2014.

The researchers also looked at whether awareness of e-cigarettes among current smokers influenced their attempts at quitting or intention to quit. They found no association. While some smokers may independently use e-cigarettes to try and quit, doctors are not advising patients to do so. They typically suggest trying nicotine patches or chewing gum.

Smokers who perceived e-cigarettes as less harmful than traditional cigarettes were less likely to have attempted to quit in the previous year.

More information: "Trends in E-Cigarette Awareness and Perceived Harmfulness in the U.S." was written by Timothy R. Huerta, Daniel M. Walker, Deborah Mullen, Tyler J. Johnson and Eric W. Ford. Journal information: American Journal of Preventive Medicine "Trends in E-Cigarette Awareness and Perceived Harmfulness in the U.S." was written by Timothy R. Huerta, Daniel M. Walker, Deborah Mullen, Tyler J. Johnson and Eric W. Ford.