Once hailed as the healthier end-all to smoking traditional cigarettes, public officials are becoming increasingly more concerned about e-cigarettes, especially in youth populations. Juul in particular has sparked heated debate since its launch of sleek, small vapes and sweet-flavored nicotine cartridges in 2015.

In fact, the World Health Organization actually singled out Juul in its latest report on the global tobacco epidemic (page 31, pdf), calling it one of the new industry players that "continue to subvert tobacco control" -- so it's no surprise that big cities are taking action and banning e-cigarette sales in an attempt to keep their residents healthy. 

So are the Juul and other e-cigs bad for you or not? The evidence remains inconclusive because, unlike traditional cigarettes, e-cigarettes haven't been around long enough to make conclusive "x equals y" claims. However, there's plenty of reason to believe that some of the same perils apply. Below, doctors weigh in on the most significant health risks. 

Read more: Is Juuling bad for your teeth? | How to quit Juul-ing, according to addiction experts 

Scientists don't know everything about e-cigarettes yet, but they do know that many of the same perils associated with conventional cigarettes still apply.

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Heart attack, stroke and coronary artery disease

In May 2019, the Stanford School of Medicine released a study showing that the e-liquids in Juuls and other e-cigarettes could increase a person's risk of heart disease by damaging the endothelial cells that line the interior of blood vessels.

When researchers exposed these cells to e-liquids, they began to show signs of dysfunction and disrepair, including DNA damage and cellular death. The scientists tested the endothelial cells by exposing them directly to e-liquid and blood collected from people who smoke e-cigarettes, and the damage occurred in both settings.

The Stanford researchers used human endothelial cells that they grew from stem cells, an ideal method for studying cells that are hard to isolate from patients.