I'll bet there's absolutely no proof of that. Just some slap-dash studies where a tiny bit of correlation is taken to be causation.
Time to bring this site out again.
http://www.davehitt.com/facts/who.html
” Breathing it in can damage lungs and cause cancers, research has shown.
I’ll bet there’s absolutely no proof of that.”
Harvard Med did a study 20 years ago, that proved second-hand smoke was harmless....just an eye irritant. It was reported once, and buried for eternity : )
Or even when there probably is causation, the risk increases from 1 in 100 million to, gasp, 10 in 100 million or something and of course they report that as "a tenfold increase in risk". (Which it is, but who cares, given the absolute magnitude of even the new, increased risk.)