ID=9859047ATLANTA -- More than 40 million Americans have used e-cigarettes, but a new study shows the liquid inside damages healthy cells and increases your risk of respiratory infections.

Researchers at National Jewish Health in Denver tested the liquid used in e-cigarettes, sometimes called e-liquid. They found the liquid quickly damaged healthy cells. Doctor Hong Wei Chu led the study. His team put cells from the airways of healthy, young, non-smokers in one end of a device and an e-cigarette in the other.

"It increased the level of viral infection inside the cells," Chu said. In fact, they found after just ten minutes of exposure, the cells were damaged. That damaged lasted 24 hours or longer. The study showed it didn't matter if the liquid contained nicotine or not, the liquid itself did the damage.

Researchers say the findings are especially troubling since some e-cigarettes are flavored to appeal to younger users. "When you flavor them that way, not only are they appealing, but, falsely, the user sees them as 'Oh, no big deal. They're not bad for me.'"

Over the next week, millions of Americans will make New Year's Resolutions to quit smoking. Many will turn to e-cigarettes as a method to help. Over the last year, as sales topped $3.5 million, concerns about safety are also on the rise. In July, the World Health Organization found there was not enough evidence to determine if electronic cigarettes really help people quit smoking. The World Lung Foundation is recommending tighter regulation of e-cigarettes due to those growing concerns.