There is a rift in the world of e-cigarettes, and both sides are public-health experts.

In the United States, tobacco-control advocates have taken a hard line on e-cigarettes, treating them as no different and no safer than regular cigarettes. Across the pond, top U.K. doctors and health authorities have a more permissive stance, suggesting e-cigarettes as a safer alternative to cigarettes. They’re both right, in a way, and the debate is really over who you're focusing on when you ask if e-cigs are safer—smokers or non smokers?

E-cigarettes vaporize liquid that usually contains nicotine, and they do not involve any burning of tobacco—which eliminates the smoke that causes most of cigarettes’ ill effects. So in a strict comparison of e-cigarettes and cigarettes, the former is not as dangerous. In the U.K., public-health officials want to use e-cigarettes to get people to quit smoking. In the U.S., officials worry that e-cigarettes will entice new users, who would have never gotten addicted to nicotine otherwise.

It’s in this context that the U.S. surgeon general, Vivek Murthy, today issued a report on e-cigarette use in teens and young adults—the most critical demographic if you’re worrying about new users. The report is unequivocal in its warnings. E-cigarette use among high school students in the U.S. has grown 900 percent since 2011, as vape shops have become ubiquitous. The report also laid out the scientific evidence that young people with developing brains are particularly sensitive to nicotine, which is a highly addictive substance.  And it criticized the industry for marketing to teens with candy-flavored vape juice.

What it does not do—simply because not enough time has passed to generate the data—is definitively say whether e-cigarettes are replacing cigarettes for teens or simply getting more of them addicted to nicotine.

If you’re worried about nicotine-addicted teens, then waiting until the data is clear will be too late. “We have a narrow window to act to implement proven policies that can prevent adolescent use. We can’t let that window close,” says Erika Seward, the assistant vice president for advocacy for the American Lung Association, which has hailed the surgeon general’s report. So much will hinge on whether teenagers think vaping is some nebulous idea of cool. Once attitudes are set, good luck having some lame adults convince teens of anything.

So the report from the surgeon general’s office today about e-cigarettes is an attempt to frame the conversation on its terms. And sure enough, the report spurred a wave of headlines warning against e-cigarettes. The accompanying website also has a section instructing parents how to talk to their kids about the issue.

With their explosive growth in the last five years, e-cigarettes have surpassed cigarettes as the most commonly-used tobacco product among youth. And the report notes that “e-cigarette use is strongly associated with the use of other tobacco products among youth and young adults, including combustible tobacco products.” But “associated” means the causation can run in either direction. If vapers are also more likely to have used regular cigarettes, it could mean they used e-cigarettes to quit smoking or it could mean e-cigarettes were a gateway to regular smoking. In fact, the two sides have argued it both ways.

E-cigarettes pose a challenge for public health messaging. Mike Siegel, a tobacco control and public health researcher at Boston University, has advocated for e-cigarettes as a replacement for smoking, and he thinks federal officials should convey the risks of the different products. “I don’t think the public is that stupid. I think they are able to differentiate between different degrees of risk,” says Siegel. He points to alcohol as an example of how the CDC threads the needle on communicating different levels of risks: Moderate drinking is okay, but binge drinking is not.

Messaging that is too blunt can also backfire, as it did for a CDC recommendation on alcohol earlier this year. The agency released an infographic advising women to avoid drinking if not on birth control—owing to the danger alcohol can pose to the fetus before the woman even knows she’s pregnant—and that turned into a firestorm. The recommendation was widely pilloried as sexist and paternalistic. It was clumsy messaging, an attempt to mitigate all hypothetical risk without accounting for the real world tradeoffs.

E-cigarettes are novel enough that public opinion on them might still be malleable. Are they yet another tobacco product from an industry that’s made billions off of addicts and, in cases, quite literally killed its customers? Or are e-cigarettes something new, something that could forge a different reputation? Both sides see this as a critical time for figuring out the message on e-cigarettes. Public health campaigns, however well-intentioned, are still PR battles.