BROOKLYN (VosIzNeias) — Health officials have long debated whether vaping leaves any deleterious health effects , but a new study using mice suggests that long-term exposure to vaping liquids that contain nicotine greatly increases the risk of cancer.

The study revealed that for the mice which breathed in the vapor for 20 hours a week for more than a year, 22.5% had cancerous tumors in the lining of the lungs, and 57.5% developed growths in their bladder tissue that can be precursors to cancer.

On the other hand only 5.6% of the mice in a control group that breathed only filtered air wound up with lung tumors, and none had growths in their bladders. In addition, a group of mice exposed to aerosolized vaping chemicals without nicotine developed no lung tumors, and just 6.3% of them had precancerous bladder growths.

The scientists who conducted the study stressed that much more research is needed to know whether vaping leads to cancer in humans. But they hope their findings, which were published Monday in the journal Proceedings of the National Academy of Sciences, will make people think twice before trying e-cigarettes, which are widely perceived by teenagers and young adults as a safe alternative to smoking.

“Right or wrong, millions of young people are using these right now, and the long-term, population-wide studies won’t be able to report out results for another decade,” said study leader Moon-Shong Tang, an environmental health expert at NYU School of Medicine.

“We needed credible evidence to guide people in their choices, and it is unambiguous that nicotine alone will cause damage to the cells that make up organs, including lungs,” said Tang, who has studied how tobacco smoke promotes cancers of the lung and bladder. “Now, we can try to find measures to prevent incidents of e-cigarettes causing cancer.”

Even though some health authorities have encouraged vaping as a way for people to quit potentially deadly levels of smoking, vaping itself has been linked to heart attacks, seizures and burns from exploding devices. And a growing mysterious outbreak of at least 1,080 vaping-related lung injuries demonstrates that it’s still too soon to know whether e-cigarettes are a safe alternative to smoking.