The University of South Carolina and the Medical University of South Carolina are among research institutions investing in research on the public health effects of e-cigarettes. A national review recently concluded teens who begin smoking e-cigarettes are likely to move on to the combustible type.

Ask researchers whether e-cigarettes are good or bad, and you’ll rarely get a straight answer.

They are good in some instances and known to be bad in others. But the long-term effects of the popular devices are still unknowable. Researchers are rushing to tackle the most trying questions about the effects of e-cigarettes on short- and long-term public health.

“E-cigarettes cannot be simply categorized as either beneficial or harmful,” said David Eaton of the University of Washington, chair of the committee that wrote a congressionally-mandated report on e-cigarette use, in a prepared statement.

Anthony Alberg, a researcher at the University of South Carolina, contributed to that report. It was released last month.

Research into e-cigarettes is fueled by a need for answers as to whether e-cigarettes will lead people to — or away from — combustible cigarettes, known to be disastrous for a person’s health.

A review in the British medical journal BMJ recently showed even smoking one combustible cigarette a day increases risk of heart disease and stroke.

E-cigarettes were popularized in the mid-2000s, and have attracted more young people than old. They work by heating a liquid that can be bought in certain stores. The result is a vapor the user inhales through a mouthpiece. Because the devices do not burn tobacco, they are considered likely to be healthier than combustible cigarettes.

Research was released in 2015 showing how teen use of cigarettes had dropped, even as their use of e-cigarettes climbed. But experts were still concerned young people could be starting with the e-cigarettes and moving on to the combustible version.

Alberg’s research group found conclusive evidence this is the case.

“Everything is pointing in the wrong direction right now to raise a red flag about the public health impacts of e-cigarettes,” said Alberg, an epidemiologist.

He said it is still unclear if those young people progress to a nicotine addiction. He stressed this is the long-term impact researchers should focus on, and for now, those effects are difficult to know.

Still, the national review concluded there could be benefits for public health in the near term, especially for adult cigarette smokers.

Experts at the Medical University of South Carolina were able to show with a pilot study published late last year that smokers they provided with e-cigarettes were more likely to quit smoking the combustible type. Matthew Carpenter, co-director of tobacco research program at MUSC, said the group studied 68 local smokers.

Two groups were given e-cigarettes, one with a more powerful dose of nicotine than the other.

The research subjects could use the vaping contraptions however they wished.

Carpenter said his research group will next start a similar study on a national scale.

They will enroll 650 subjects across the country.

Carpenter also said e-cigarettes could be viewed as being bad for some, while good for others.

“We can’t come to a simple, one-sentence answer,” Carpenter said.

“There’s potential for great public health benefits, but there’s also potential for harm.”