When e-cigarettes hit the market they seemed like a godsend to smokers (and maybe even curious non-smokers): all the enjoyment of smoking cigarettes and none, or at least far fewer, of the health risks. You're only breathing in water vapor and pure nicotine, the ads said.

But have those claims held up since e-cigarettes were introduced to the U.S. and European markets 10 years ago? The science is a bit more complicated than it seems, with scientists doggedly fighting to heavily regulate e-cigarettes, and others touting them as the ultimate smoking cessation device. Who is right?

The Daily Dot dug into the science to try and answer this question. But, spoiler alert: The science behind e-cigarettes is young and inconclusive. They currently are not regulated by the Food and Drug Administration, which essentially allows e-cigarette manufacturers to operate without much oversight on nicotine contents and other chemical components in their e-cigarette liquids. However, the FDA will begin regulating e-cigarettes in August 2016.

Cancers, lung disease, and heart disease all take several years to develop — people haven't been using e-cigarettes long enough to develop these diseases. Also, most e-cigarette users (called "vapers") are current or former smokers, so it will be hard to parse out whether smoking or vaping was the true culprit of whatever diseases do form. Researchers can study the effects of e-cigarette aerosol in cultured cells and lab animals, but those studies can't definitively tell us what real-world e-cigarette use will look like in the long term. Lastly, several researchers are attempting to answer the question of whether or not e-cigarettes can be used to quit smoking all together. But that question has a complicated, incomplete answer too.

Let's break it down, starting with the physical differences between traditional and e-cigarettes.

Combustion vs. vaporization

Much of what makes traditional cigarettes so dangerous isn't the nicotine — nicotine is super addictive, and can cause heart disease, but there's very little evidence that it causes cancer. Cigarettes are dangerous because of the smoke itself. Lighting up causes the tobacco leaves and cellulose paper they're wrapped in to combust. And combustion of plant matter releases several other chemicals: aldehydes, carbon monoxide, free radicals, heavy metals — a combination that can cause not only cancer but lead to heart and lung diseases as well.

E-cigarettes, on the other hand, use a battery to vaporize a mixture of nicotine, glycerol or propylene glycol, and flavorings, depending on the product. Vaporization happens at a much lower temperature than combustion, so it seems reasonable that it wouldn't cause the release of all the same nasties as cigarettes.

But you're not just breathing in nicotine and water vapor, according to Stanton Glantz, professor of medicine and director of the Center for Tobacco Control Research and Education at the University of California, San Francisco.

"In the process of heating up [e-cigarette liquid,] you get a lot of aldehydes and the ultrafine particles are themselves dangerous," Glantz told the Daily Dot over the phone. "The cancer risk is probably lower than a conventional cigarette, but the effects of the ultrafine particles and the aldehydes are about the same."

The effects of the particulates may include inflammation in the lungs that can cause lung disease over time. One study found that cultured white blood cells exposed to e-cigarette vapor extract released inflammation-causing compounds, suggesting that breathing e-cigarette vapor may have similar effects within the body. Glantz also said that the particulates in both e-cigarette vapor, cigarette smoke, and air pollution can also cause the blood to get "sticky," leading to clogged arteries and heart disease.

The preliminary evidence agrees with Glantz's views. According to two reviews, e-cigarette vapor is quite harmful in animal and cell culture studies. However, detractors from e-cigarettes tend to argue that e-cigarettes also release aldehydes — but there's reason to be skeptical, according to the second review. One study found that e-cigarette vapor contained formaldehyde — the same probable-cancer-causing chemical used to preserve animals for dissection. However, some argued that the temperature used to create the e-cigarette vapor in that study was too high. Vaping at too-high temperatures causes a phenomenon called a "dry puff" which is very harsh and unpleasant, as anyone who's ever tried an e-cigarette can tell you.

According to a recent study in the journal Addiction, e-cigarettes only release formaldehyde in the "dry puff" condition.

E-cigarettes are a moving target

In the 10 years they've been on the market, e-cigarette devices have changed rapidly. The first generation e-cigarettes looked a lot like traditional ones (they're also known as "cigalikes"), but weren't as good at getting nicotine into the blood as traditional cigarettes.

But the newer generation e-cigarettes deliver nicotine to the bloodstream at levels comparable to regular cigarettes, meaning they can give vapers the same nicotine fix as smokers. This is good news for their potential to help smokers quit smoking. But there's a catch.

"Most of the data I've seen on second and third-generation devices is that they do cause inflammation in the lungs. They do cause a measurable biological response," Robert Teran, lead author of the second review and director of SoM Tobacco Center of Regulatory Science at the University of North Carolina, Chapel Hill said in a phone interview with the Daily Dot. "Time will tell whether or not that chronic inflammation will lead to disease."

Additionally, e-cigarettes introduce a few variables that traditional cigarettes do not. Flavorings are common in e-cigarette liquids. While the chemicals used to create those flavors are all on the FDA's approved list of food additives, pretty much no one has studied the effect of inhaling the vapors of these chemicals, Teran said.

There is one notable exception: diacetyl. Diacetyl is the primary chemical that gives movie theater popcorn its buttery flavor. It's also a byproduct in many other foods: it gives some Chardonnays their signature buttery undertones. If you pick it up in beer, that can also be a sign that your local bar needs to clean the lines in their beer taps.

"It's safe to eat, but if you breathe it in it causes bronchiolitis obliterans," otherwise known as popcorn lung, Teran said. And the only reason researchers know about the harmful effects of breathing in diacetyl is because workers in popcorn factories came down with this illness.

But diacetyl isn't just in buttery flavors. It's also in a lot of berry flavorings as well, according to one study found diacetyl in 39 of 51 e-cigarette flavors. However, diacetyl is also present in cigarette smoke — at levels higher than those experienced by workers in popcorn factories, according to a 2014 study. So maybe it's a wash with diacetyl.

Nonetheless, there are still many compounds in e-cigarette flavorings whose effects on the lungs are still relatively unknown. In fact, Teran believes that e-cigarettes and traditional cigarettes might have more differences than similarities, and comparing them to one another might not be the best way to assess e-cigarette's health risks. After all, being "safer than smoking" is a very low bar to clear.

Teran cited a study from his lab that found vaping was associated with suppression of genes related to the immune system. The researchers even found many suppressed genes in vapers that they didn't find in smokers, suggesting vaping may have some unique effects on the immune system.

The ultimate cessation aid?

To say quitting smoking is hard is an understatement. Nicotine isn't just highly addictive; it can literally change the development of the brain to make people even more dependent on it if they start smoking in their teens — which is exactly when most smokers start. Smokers looking to quit have a few options: cold turkey, gradually cutting back, using a nicotine replacement therapy, or a drug like Chantix.

Nicotine replacement therapy — using something like the patch or gum — helps smokers get their nicotine fix and taper them off of nicotine while keeping them from smoking. Many people may choose to go these treatments alone by buying the therapies over the counter at the drugstore.

According to a study from the '90s, quit rates for people who do the patch or gum alone, without the help of their doctor, vary between around 15 percent after six weeks, to less than 10 percent at 24 weeks follow-up. But subsequent reviews of that study and others like it that attempted to gain "real world" evidence for replacement therapies found their methodologies to be flawed.

Another review of nicotine replacement therapies found that people may be more successful if they had behavioral support such as a hotline to call or group therapy sessions. But quit rates are still low. Replacement therapy only enhances someone's chances of quitting by 50 to 70 percent, according to the review. So if someone goes cold turkey without any support and has an 8 percent chance of success, using replacement therapy is only going to make their chances marginally greater — and that's only to smokers who are very highly motivated to quit.

It's unclear why quit rates are so low with replacement therapy. But part of the issue may be that smoking is more than just nicotine: it's the ritual and social aspects too. E-cigarettes provide many of those same comforts, so some researchers believe they can be highly effective quitting tools.

"I think someone specifically comes and seeks treatment, then I would recommend Chantix or nicotine replacement treatment, possibly supplemented by e-cigarettes," Peter Hajek, Director of Tobacco Dependence Research Unit at the Wolfson Institute of Preventive Medicine in London, told the Daily Dot in a phone interview. "So many smokers only manage to stop smoking when they try a few of these e-cigarette models."

Hajek was involved in a 2014 review of e-cigarettes for smoking cessation. He and his colleagues found that e-cigarettes containing nicotine were more helpful than e-cigarettes without, but they couldn't determine if they were any better than the patch. Nonetheless, Hajek and colleagues in the Royal College of Physicians now urge smokers to make the switch to e-cigarettes, citing that they are 95 percent less harmful than cigarettes.

How they got to that number is unclear. When the Daily Dot asked Hajek about it directly, he cited the many known toxic chemicals in cigarette smoke that lead to heart disease, lung disease, and cancer.

"These chemicals are either totally absent or present in only minuscule amounts in e-cigarette vapor," Hajek said. "Chemicals exclusive to vaping may yet be found to also pose some risks, but this is unlikely to be more than only a small fraction of the risks of smoking."

But 95 percent less harmful seems like a long shot to Glantz.

"The 95 percent number … was simply made up," he said. "If you go back and find the paper that comes up with that number. It has exactly no actual evidence in it. They got six people together, several of whom had financial conflicts of interest, got around a table and scratched their head and scratched their butt and got that 95 percent number."

Glantz thinks, if anything, e-cigarettes are about "a third to a half" as dangerous. Much of Glantz's work has also been to disprove the idea that e-cigarettes are useful smoking cessation tools when used alone. Earlier this year, he and his colleague published an analysis of several studies in the Lancet that e-cigarette users were 28 percent less likely to quit smoking than those who didn't use e-cigarettes.

"The most dangerous thing about e-cigarettes is that they keep people smoking. If you were a cigarette smoker and you switched entirely from cigarettes to e-cigarettes, it would be less dangerous," Glantz said. "The majority of the data suggests most people are dual users."

He added that he believes e-cigarettes have definitely helped some people quit. But he thinks that they would only work for a minority of smokers.

Taber also thinks that e-cigarettes might not be a good cessation tool, but that they are less harmful than traditional e-cigarettes.

"If you're smoking cigarettes, going to e-cigarettes is probably better for your health," Taber said. "And if you're not smoking anything at all, don't try e-cigarettes and think they won't have an effect on your lungs."

From our friends at The Daily Dot, by Cynthia McKelvy.

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