Basically, breathing in any kind of particulates is bad for you, and very fine particles (like smoke/vapor) can pass through cell walls and interact with your proteins resulting in transcription errors during cellular reproduction. For instance, asbestos fibers can tangle with and damage chromosomes [2]. The more often you do it, and the more volume you expose your lung tissue to, the higher the odds that something will go catastrophically wrong.
Basically, breathing in any kind of particulates is bad for you, and very fine particles (like smoke/vapor) can pass through cell walls and interact with your proteins resulting in transcription errors during cellular reproduction. For instance, asbestos fibers can tangle with and damage chromosomes [2]. The more often you do it, and the more volume you expose your lung tissue to, the higher the odds that something will go catastrophically wrong.