I'm not sure if the barrier of cells is removed with time. All that tar and gunk makes the cillia overworked (they wiggle to push toxins out of lungs), and thats when the new layer of cells is created.

Acid reflux disease? Kinda the same idea - Stomach acid leads to destruction of your esophagus tissue.

I'm still pondering your ? about smokin a fresh bowl verses a beat bowl. I think a beat bowl (black bowl) would have be a little more toxic for you in regards with tar. But lighting a green bowl is still going to burn plant material, which in turn will lead to tar in the lungs. The thc/tar ratio would be higher in the green bowl than in that of the beat bowl.

The idea of the vaporizer is ingenius.................all active ingredients w/o plant matter burning and adding to a heavy/dirty smoke.