Recent reports have suggested e-cigarettes are safer than smoking traditional cigarettes, but new research from Harvard University suggests that may not be the case.

Dr. Joseph Allen led a research team at the Harvard T.H. Chan School of Public Health, testing 51 types of flavored e-cigarettes and liquids.

Some of the popular flavors, include Double Apple Hookah, Tutti Frutti, and Alien Blood.

The research found many of the flavoring liquids contain chemicals that are potentially very harmful. The most common found was diacetyl, which has been blamed for causing a condition known as "popcorn lung" in workers at microwave popcorn factories.

"We know that exposure to these flavoring chemicals has been associated with these really severe and irreversible lung disease," Allen said.

Diacetyl was found above the lab limit in 39 of the 51 flavors tested. Overall, at least one flavoring chemical was found in 47 of the 51 tested.

Other chemicals found include 2,3-pentanedione, which has caused lung and brain damage in rats, and acetoin. Acetoin has also been linked with "popcorn lung."

Allen said one of the major issues surrounding e-cigarettes is that they are very new, so there is still so much to be learned about their effects both short-term and long-term.

"We know very little about these chemicals and what are safe levels, if there are safe levels at all for these flavoring chemicals," Allen said. "Yet we have widespread exposure."

E-cigarette use has skyrocketed over the last few years with an estimated one-in-ten Americans now regularly vaping.

Allen concludes that more research still needs to be done to determine the how much of the toxins are contained in the e-cigarette oil, and how much people need to inhale to put themselves at risk.

But, the new research does serve as a new caution for vaping, which has been looked at as a safe alternative to smoking.