The study isn't completely shocking when researchers have identified other harmful chemicals. And it's not conclusive, either. While the testing shows that e-cigarettes are harmful, the highly compressed smoking exposure is far from what you'd see in real life. The study does also acknowledge that the tobacco nitrosamines (known carcinogens) found in body fluids of e-cigarette users are 97 percent lower than in cigarette smokers (but states this is "significantly higher than in nonsmokers"). This puts e-cigarette users on a similar level to users of nicotine patches.
You may not see more definitive results until additional animal testing in a year, and much longer than that for humans. Study author Moon-shong Tang also noted to Bloomberg that it's not clear whether conventional cigarettes or e-cigarettes would be more harmful.
While there have been studies suggesting that e-cigs are probably less harmful, the study indicates that some nitrosation of nicotine occurs in the human body (in cigarettes it happens in the tobacco curing process). So, theoretically, you're still facing some of the same dangers. Any "safety" therefore may come from the reduced level of exposure. The findings also support bids to regulate e-cigarettes based on their tobacco-like effects, such as the FDA's former approach.
This article has been updated to clarify the findings of the study.