E-cigarettes have increasingly been seen as a possible savior for many who struggle to kick their cigarette addiction, as the vapor is deemed much less dangerous than the tar caused by regular smoking. But a new study suggests that we have a lot to learn about the safety of e-cigarettes, and there may be dangers lurking within them.

Specifically, the team of researchers from Johns Hopkins Bloomberg School of Public Health found that e-cigarette vapor may have toxic levels of lead and other metals that are dangerous to the human body. They published their findings in the journal Environmental Health Perspectives.

The study involved analyzing vaping devices used by 56 e-cigarette smokers, and it found that many of the devices had high levels of lead, chromium, nickel, and manganese, to name a few alarming metals. Such metals are linked to health issues, including cancer of the lungs, brain, immune system, and the liver.

“It’s important for the FDA, the e-cigarette companies and vapers themselves to know that these heating coils, as currently made, seem to be leaking toxic metals—which then get into the aerosols that vapers inhale,” says study senior author Ana María Rule, PhD, MHS, an assistant scientist in the Bloomberg School’s Department of Environmental Health and Engineering.