It's debatable. Some say that if the silica you use is fragile enough- and if during use, some of the "pops" or "
juice explosions" are able to damage the silica to an extent that it ejects single fibers of silica into the air stream, those fibers (if inhaled) might be small enough that over time, they might catch and build up in the lungs, causing silicosis (basically, like a type of lung cancer that can't metastasize [spread]
throughout the body).
I personally avoid the stuff, but even things like oxidized SS (residue from butane torching) or kanthal (made up of a small amount of aluminum) have risks. Anything is better than the certainty of health effects from
tobacco smoking, though.