 It more than likely is because it heats up the solution that they use and it turns it into a vapor. The vapor has very, very tiny particles. Tiny particles are the more toxic ones because they can get really further into the lungs and into the tiny part of the lungs and can cause more problems later. That's where your body exchanges oxygen. That's how you breathe. So when that gets clogged up with tiny particles of solvents, that's not good.