It's highly likely that the performers who smoke, do so only after a performance. I know Idina practices yoga, and from experience, yoga does wonders for your voice. So, as long as she's properly readied her voice before going onstage- not that I'm advocating smoking or anything. Then again, Jarrod Emick smoked in the wings during performances of Boy from Oz.
I've heard Euan Morton live, and I really think his heavy smoking is affecting his voice negatively.
I'd be really shocked if Kristin Chenoweth smoked. For some reason, I can't see it. Then again, her voice is powerhouse, and maybe it doesn't affect her.
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