As the popularity of vaping has grown, so have the number of studies claiming e-cigarettes can be a "gateway drug" to real smoking. Some researchers say e-cigarette use makes people twice as likely to develop a tobacco addiction. Others put that number at closer to 10 times as likely.
But no matter the ratio, there are also scientists who worry these papers exaggerate the link between e-cigarette use and real tobacco use and may be misleading the public.
Some studies warn that the connections they found aren't all that strong. Researchers behind a study titled "First evidence that e-cigarettes may be prompting UK teens to try the real thing" put a disclaimer in their research, saying "no firm conclusions can be drawn about cause and effect."
And some studies have been accused of using "misleading measures" to decide who counts as a tobacco user. For instance, in one University of Hawaii survey, researchers asked about 2,300 high schoolers if they had ever smoked and then followed up with them a year later.
Researchers found that kids who had used e-cigarettes at the time of the first survey were three times as likely to be smokers in the follow-up. But they defined a "smoker" as anyone who had tried even a single cigarette during that year.
Overall, attempts to show that e-cigarettes are as harmful as actual tobacco products have fallen short. Studies seem to show that they're upwards of 95 percent safer, and can actually be a useful tool in helping people quit smoking cigarettes.