Is vaping the lesser of two evils compared to smoking or just a newer, shinier health threat?

To some public health experts who’ve seen adult smokers hooked on tobacco despite its death toll from cancer and heart disease, e-cigarettes have the potential to reduce harm by helping them quit. But others who see kids pick up vaping and potentially developing nicotine habits are less hopeful and more concerned.

[See: 7 Things You Didn’t Know About Lung Cancer.]

Internationally, public health and medical communities remain divided, Dr. Stephen Amrock, with Oregon Health & Science University, writes in an email. “British authorities, for example, advocate e-cigarettes as a harm-reduction tool, theorizing that the unknowns about e-cigarettes outweigh the known concerns with other tobacco forms,” says Amrock, who has conducted research on teens’ perceptions of e-cigarettes.

E-cigarettes normally work when the battery-operated devices generate heat to create vapor from sealed cartridges. Cartridges and liquid refills contain varying amounts of nicotine, or none at all.

In January, a systematic review from Canadian scientists at the University of Victoria’s Centre for Addictions Research of BC found that e-cigarettes are less harmful than tobacco, with vapor emissions containing about one-fourth of the toxins and none of the tar found in cigarette smoke. Vaping also reduces exposure to secondhand cigarette smoke, researchers found.

However, less harmful doesn’t mean harmless. “Recent research also suggests that e-cigarette users have physiologic changes similar to those who smoke cigarettes,” Amrock says. “Cholesterol, heart-rate variability and blood pressure all worsen, leaving blood vessels susceptible to damage similar to what cigarettes do.”

For motivated adults who want to quit using tobacco, data suggest e-cigarettes can be a useful stepping stone, Amrock says. However, he adds, “These results showed that nicotine-based e-cigarettes don’t perform any better than existing, regulated nicotine-replacement strategies.”

The catch is that nicotine patches and gum aren’t nearly as popular as e-cigarettes, says Thomas Brandon, head of the Health Outcomes and Behavior Program with the Moffitt Cancer Center in Tampa, Florida. “In terms of a larger public-health perspective, a lot more people are using e-cigarettes than are using those nicotine-replacement products,” Brandon says. “So it might be something we want to capitalize on.”

[See: 8 Questions to Ask Your Pharmacist.]

The e-cigarette issue is polarizing within the U.S. as well. “Nothing has divided the tobacco-control field like this has,” Brandon says. “It’s almost brother against brother. It’s amazing. It’s sometimes mentor versus mentee.”

Brandon has spent more than three decades immersed in research on smoking cessation in adults. He’s now conducting a two-year study on dual users — people who both smoke tobacco and use e-cigarettes.

Brandon’s research team is pitting two theories against each other. One is that vaping will really help people quit smoking and that dual users will eventually give up tobacco, and maybe even e-cigarettes at a later point. The second theory is more pessimistic: Smokers will maintain dual use because vaping makes it more convenient, allowing them to get their nicotine hits in situations where they can’t smoke, such as in the house or certain public places.

The No. 1 reason smokers in his study start vaping is to quit cigarettes, Brandon says. “What we want to find out is: Does it actually work?”

Smoking kills nearly half a million Americans each year, according to the Centers for Disease Control and Prevention. “We don’t know the answer yet,” Brandon says. “But there’s a potential for e-cigarettes to have a tremendous disruptive effect on smoking and a huge effect on public health.”

Younger Vapers

Yet the following research, released online or published in the February print issue of the journal Pediatrics, suggests vaping isn’t benign for young people, who may be attracted by its novelty and kid-friendly flavorings such as fruit punch and bubblegum.

— An anonymous survey of more than 7,000 Connecticut high school students found that of the 1,080 who’d ever used e-cigarettes, about one-quarter had tried “dripping” with them. That’s when users inhale vapor made by dripping e-liquid directly onto heated coils of e-cigarette devices. Exposing e-liquids to higher temperature increases the level of toxic chemicals formed in the vapor, researchers noted. Among students surveyed, reasons for dripping included, “It makes the flavor taste better,” “It makes a thicker cloud of vapor,” “It makes a stronger throat hit” and “I was curious.”

— Data from more than 15,000 participants in the 2015 national Youth Risk Behavior Survey showed that e-cigarette use, by itself or with cigarette smoking, was associated with more health-risk behaviors among high school students. Injury, violence, substance use and sexual activity were more likely among vapers, found researchers led by Dr. Brian King, with the CDC’s Office on Smoking and Health.

— A study from the Center for Tobacco Control Research and Education at the University of California–San Francisco found many adolescents in grades six through 12 who had never smoked and were otherwise considered at low risk for starting to smoke had used e-cigarettes, raising the specter of vaping as a gateway to smoking.

The gateway scenario is supported by an August 2015 study published in JAMA, which followed some 2,500 ninth-grade students from 10 Los Angeles high schools. Those who had ever used e-cigarettes were more likely to have started smoking cigarettes within the next year. It’s difficult for parents or teachers to monitor e-cigarette use or contents, points out study author Dr. Adam Leventhal, director of the University of Southern California Health, Emotion and Addictions Laboratory. The vapor is odorless and dissipates quickly on exhalation.

“A teen can be in the back of a classroom sneaking a vape,” Leventhal says. “And we don’t know whether they’re just vaping a substance that has no drugs in it, just for fun and the flavor. We don’t know if it’s nicotine. We don’t even know if it’s THC — the active compound in marijuana.”

Although nicotine-free products are available, kids may be using nicotine without realizing it. “It’s questionable whether kids know what nicotine is, let alone whether it’s in the products that they’re using,” King says. “So we’ve turned to more objective sources of monitoring this, including retail sales data. And those data show that the vast majority of e-cigarette products on the market contain nicotine.”

An ongoing study is looking at exposure to toxins from e-cigarette vapor in teen users. “I’m testing their urine and saliva for nicotine byproducts,” says researcher Dr. Mark Rubinstein, a professor at the University of California–San Francisco School of Medicine. “And I’m also testing their urine for levels of toxicants.” Toxicants are naturally occurring yet harmful toxins, like benzene, that can form with e-cigarette use and have been found in the urine of adult users.

“The problem is when you heat propylene glycol and glycerin together, depending how high a temperature, it can form formaldehyde,” Rubinstein explains, of the major components of vape “juice.”And the glycerin can form acrolein, which is associated with lung cancer.”

[See: 10 of the Biggest Health Threats Facing Your Kids This School Year.]

For parents, King says, it’s not a question of whether e-cigarettes are preferable to traditional cigarettes. “From the youth standpoint, we’re really talking about one of prevention as opposed to kids using one product that may have less harmful constituents,” he says. “The bottom line is that none of these products are safe for youth to use.” The CDC offers these tips for parents on talking with teens about e-cigarettes.

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Revisiting E-Cigarettes: Safe or Harmful? originally appeared on usnews.com