A new study found that people who vape may be inhaling potentially dangerous levels of toxic metals like lead. Most research suggests vaping is a healthier alternative to smoking, especially for adults who want to quit. But those studies have also revealed some of its potential downsides.

In addition to inhaling burned tobacco and tar, smokers breathe in toxic metals like cadmium and beryllium, as well as metallic elements like nickel and chromium — all of which accumulate naturally in the leaves of the tobacco plant.

Most of the available evidence suggests that vaping, which involves puffing on vaporized liquid nicotine instead of inhaling burned tobacco, is at least somewhat healthier.

In 2015, a group of researchers from medical schools across the globe decided to find out just what was inside the vapors that e-cig users were inhaling.

Trapped deep in the aerosol particles that vapers breathe were some of the same toxic metals and metallic elements found in conventional cigarettes, including cadmium and nickel. They also found potentially unsafe levels of several other dangerous substances such as arsenic, chromium, and manganese.

They published their findings  in the journal Environmental Health Perspectives.